FOUS30 KWBC 050832
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
432 AM EDT Tue Aug 5 2025

Day 1
Valid 12Z Tue Aug 05 2025 - 12Z Wed Aug 06 2025

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHEAST AND INTO THE MID-ATLANTIC...

...Southeast and Mid-Atlantic...

A heavy rainfall and flash flood event may be getting started at
the beginning of the period, as convection is expected to increase
in coverage and intensity from northeast Georgia into Upstate
South Carolina (potentially extending into far southwest North
Carolina) this morning. A conducive overall setup for locally heavy
downpours exists, with a low-level front/convergence zone and the
right entrance region of a strong upper-level jet streak
superimposed over the same area (along with anomalously high
moisture and PWs over the 90th percentile). The main limiting
factor for organized heavy rainfall is certainly instability,
though a modestly strengthening low-level jet (15-25 kts) will
provide some isentropic upglide to kick things off this morning
(with hourly totals likely limited to 1-2"). Most hi-res models
depict a break in the precipitation during the day, but another
round may ensue later tonight over some of the same areas, as the
frontal zone and parent trough to the west move very little.

Further diurnally-driven development is expected within the broader
warm sector from the central Gulf Coast to south-central Georgia,
and the rest of South Carolina, with stronger instability building
today with daytime heating and PWs in excess of 2 inches. Hi-res
models continue to indicate fairly high probabilities of 2"/hr
rain rates, and a complex pattern of cell mergers and colliding
outflow boundaries and sea breezes. This may lead to periods of 1-2
hours where convection is maximized in particular areas, and
scattered instances of flash flooding. The inherited Slight Risk
was expanded a bit to cover coastal portions of SC/GA with the
highest probabilities for localized 5" exceedance.

...Northern Plains and Minnesota...

There continues to be a fairly strong signal for storms to initiate
in the northern extent of an instability plume in the Plains, near
the nose of a moisture transport maximum, in the afternoon today.
Consensus among the hi-res models is this will rapidly organize
into an MCS and then likely propagate quickly to the southeast in
the general direction suggested by the thickness contours. The
potential for relatively fast forward motions may mitigate some of
the flash flood risk. However, precipitation anomalies over the
past 14 days indicate the pattern has been relatively wet of late
in the Northern Plains, and precipitable water values will be
anomalously high. Deep moisture combined with strong instability
should support high instantaneous rain rates. Therefore, any areas
where the duration of heavy rain could be lengthened (such as
backbuilding along the periphery of a cold pool, cell mergers with
antecedent convective development) may lead to flash flooding. The
Marginal Risk was maintained and adjusted southward based on the
latest guidance (factoring in upwind propagation favoring southern
propagation late).

...Ohio River Valley...

An inherited Marginal Risk was maintained and adjusted slightly
for a potential repeat of the pattern from yesterday, just
displaced slightly to the east over S IN, C KY, SW OH. A slow
moving mid-level wave is expected to continue to slowly shift
east, in the presence of relatively strong instability. Therefore,
scattered afternoon thunderstorms are expected. Although moisture
levels are not expected to be anomalously high, storm motions
should be very slow with mean winds in the lowest 8-km around 5 kts
or so. This could lead to localized flash flooding by extending the
duration of heavy rain with the most intense storms. Rain rates
should reach the 1-2"/hr range.

Churchill/Lamers


Day 2
Valid 12Z Wed Aug 06 2025 - 12Z Thu Aug 07 2025

...THERE ARE MARGINAL RISK AREAS FOR EXCESSIVE RAINFALL ACROSS
PORTIONS OF THE UPPER MISSISSIPPI VALLEY AND FOR THE COASTAL
SOUTHEAST AND MID-ATLANTIC REGION...

...Upper Mississippi Valley...

A region of anomalously high moisture, with PWs near the 90th
percentile, should shift east during the Day 2 period, and
generally continue to be superimposed with moderate to strong
instability on the periphery of a ridge. Confidence in the
convective details remain low at this time, but the overall
environment will remain supportive of organized convection with
high instantaneous rain rates. The pattern may still lead to a forward-propagating MCS, which would mitigate flash flood risk
overall, but the overall environment is favorable enough to
continue to maintain a Marginal Risk across the region.

...Coastal Southeast and Mid-Atlantic...

Confidence remains relatively low in the placement of the heaviest
rainfall on the Day 2 period, as the ECMWF/ECENS suite continues
to concentrate QPF farther north (mostly across North Carolina)
whereas the bulk of the other global models and ensembles are
focused south and east (mainly in SC and GA). Regardless of the
precise details, a plume of anomalously high precipitable water
values is likely to remain present across the coastal Southeast
and Mid-Atlantic region into the Day 2 period, and the flash flood
threat areas will likely come down to mesoscale details that will
come much more into focus in subsequent outlook periods.

Churchill/Lamers


Day 3
Valid 12Z Thu Aug 07 2025 - 12Z Fri Aug 08 2025

...THERE ARE MARGINAL RISK AREAS FOR EXCESSIVE RAINFALL ACROSS
PORTIONS OF THE UPPER MISSISSIPPI VALLEY AND NORTHERN PLAINS, AS
WELL AS FOR THE COASTAL SOUTHEAST AND MID-ATLANTIC REGION...

...Upper Mississippi Valley and Northern Plains...

An inherited Marginal Risk area was maintained and adjusted across
North Dakota and surroundings, as models are in good agreement in
indicating a potent upper-level shortwave digging southward into
the CONUS by Day 3. The approach of the trough is likely to result
in another wave of low-level return flow into the Northern High
Plains, sending PWs to the 90th percentile or higher once again.
Moderate to strong instability is expected to build once again with
daytime heating on the periphery of a ridge, and organized
convection is likely to ensue in the late afternoon and evening.

...Coastal Southeast and Mid-Atlantic...

Confidence remains low in the placement of the heaviest rainfall
going into the Day 3 period, with substantial differences still
between the global model suites. As anomalously high tropospheric
moisture is likely to remain near the coast, maintained an
inherited Marginal Risk area across portions of the area most
likely to realize heavy precipitation with daytime heating.

Churchill
$$
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FOUS30 KWBC 060817
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
417 AM EDT Wed Aug 6 2025

Day 1
Valid 12Z Wed Aug 06 2025 - 12Z Thu Aug 07 2025

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE COASTAL SOUTHEAST AND SOUTHERN MID-ATLANTIC REGION...

...Coastal Southeast and southern Mid-Atlantic...

Relatively high coverage of convection is expected once again
today, as a stalled frontal boundary remains draped across the
region. While storms should generally remain relatively short-lived
over any one location with shear being the main limiting factor,
more significant convective organization is possible in the
vicinity of the NC/SC Coastal Plain border region where deep layer
shear is progged to be closer to 20-30 kts (versus less than 20 kts
from surroundings). This is due to the slow eastward progress of
the blocked upper trough to the west, and a vorticity maxima may
also contribute to convective proliferation later today via DPVA
and enhanced upper divergence via right-entrance region of ~80 kt
jet streak over the Northeast. While the 00z HREF 5" exceedance
probs are quite high (50%+ over portions of the Coastal Plain),
uncertainty remains high with regard to the extent of resulting
flash flooding, as the QPF spread between the HREF members remains
quite large (with the NAM-nest and FV3 being the wetter outliers,
while the ARW and ARW2 are the drier outliers). Maintained the
inherited Slight Risk, and a targeted upgraded Moderate Risk could
be possible later today should models come into better agreement.

...Central Plains into Middle and Upper Mississippi Valley...

A mature MCS is diving southward early this morning from SD/MN into
IA/NE (see MPD #877 for more information) along with anomalously
high tropospheric moisture (PWs nearing 2.0", or around the 90th
percentile). Maintained a Marginal Risk for lingering convection
associated with the MCS this morning, along with the potential
sustained or redeveloped convection in association with the remnant
MCV later today.

Churchill


Day 2
Valid 12Z Thu Aug 07 2025 - 12Z Fri Aug 08 2025

...THERE ARE MARGINAL RISK AREAS FOR EXCESSIVE RAINFALL ACROSS
PORTIONS OF THE NORTHERN PLAINS, AS WELL AS FOR THE COASTAL
SOUTHEAST AND SOUTHERN MID-ATLANTIC REGION...

...Northern Plains...

Models continue to indicate a potent upper-level shortwave digging
southward into the PacNW by Day 2, and have maintained a Marginal
Risk centered on ND where convection is anticipated to initiate in
the afternoon. The approach of the trough will result in another
round of low-level return flow into the Northern High Plains,
sending PWs to near (or above) the 90th percentile once again.
Moderate to strong instability with daytime heating should yield
organized convection by late afternoon/evening, and a targeted
Slight Risk upgrade may be necessary with subsequent outlooks.

...Coastal Southeast and southern Mid-Atlantic...

Confidence in the rainfall forecast is relatively low going into
Thursday, as much depends on how convection ultimately evolves
today. That said, the recent trends in QPF have been downward with
most models showing anomalously high tropospheric moisture and
low-level convergence shifting to the immediate coastline. Have
maintained an inherited Marginal Risk for this cycle, which may be
further reduced in coverage should these model trends continue.

Churchill


Day 3
Valid 12Z Fri Aug 08 2025 - 12Z Sat Aug 09 2025

...THERE ARE MARGINAL RISK AREAS FOR EXCESSIVE RAINFALL ACROSS
PORTIONS OF THE NORTHERN PLAINS AND UPPER MISSISSIPPI VALLEY, AS
WELL AS FOR THE COASTAL SOUTHEAST AND SOUTHERN MID-ATLANTIC REGION...

...Northern Plains into Upper and Middle Mississippi Valley...

Inherited Marginal Risk was expanded to include a relatively large
portion of the north-central portion of the CONUS, a continuation
of the threat from Day 2 from a potent upper trough/closed low.
Convective details remain quite fuzzy at this range, but guidance
suggests the potential for localized 3-5" totals (high spatial
spread in these depictions) which may necessitate future targeted
upgrades.

...Coastal Southeast and southern Mid-Atlantic...

Low confidence forecast continuing into Day 3, maintaining a
Marginal Risk area that is largely focused on the same area. At
this juncture most models depict heavy rainfall remaining largely
offshore, but given recent heavy rains and the potential for
significant amounts today have opted to keep the Marginal Risk.

Churchill
$$
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FOUS30 KWBC 071142
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
742 AM EDT Thu Aug 7 2025

Day 1
Valid 1125Z Thu Aug 07 2025 - 12Z Fri Aug 08 2025

...THERE ARE MARGINAL RISK AREAS FOR EXCESSIVE RAINFALL ACROSS
PORTIONS OF THE NORTHERN PLAINS...UPPER MIDWEST/GREAT LAKES...AS
WELL AS THE SOUTHEASTERN COAST INTO NORTHERN FLORIDA...

...Northern Plains...

The 00Z model consensus shows a potent upper-level shortwave
tracking through the northern Rockies today/tonight with a lead
mid-level impulse out head helping to ignite thunderstorms over
eastern Montana with movement into North Dakota this
afternoon/evening. 00Z GFS forecast standardized anomalies of PW
are +2 to +3 over the northern Plains with moderate to strong
CAPE and increasing upper level divergence/diffluence ahead of the
approaching upper trough. 850 mb winds are forecast to increase
into the 30-40 kt range across SD, ahead of a related surface low,
helping to fuel the potential for multiple rounds of thunderstorms
through the period and some 2 to 4 inch rainfall totals (locally
higher possible). While movement of any organized convective
clusters should be generally be progressive toward the
east/southeast, potential for training will exist on the
southwestern flank and the environment will likely support 1-2
in/hr rainfall rates.

...Upper Midwest...

1124Z Update: Expanded the Marginal Risk area a bit west-southwest
based on the latest observational trends. Veering late-stage LLJ
(southwesterly ~25kts) orthogonal to the elevated frontal boundary
along the northeast periphery of the upper ridge has resulted in
some upscale growth with the backbuilding/training convection across south-central and southeast IA this morning. A bit later than
normal given the nocturnal-diurnal cycle transition, however in
this case the elevated convergence became maximized late given the
orientation of the veering LLJ and the frontal zone. For further
details, please refer to the latest Mesoscale Precipitation
Discussion or MPD #880.

Hurley

Previous discussion...
Thunderstorms are likely to develop during the afternoon hours in
the vicinity of Iowa/Wisconsin/Illinois with weak warm advection
across a subtle theta-e gradient that strengthens with daytime
heating. Moderate to strong instability is forecast to develop from
southern Minnesota into Iowa and points eastward at the nose of a
20 to 30+ kt 850 mb jet axis oriented southwest to northeast into
the Upper Midwest and continue into the first half of the
overnight. While uncertainty remains, indications are for a small
cluster of thunderstorms to form with potential for upstream
development and slow net movement of heavy rain cores. 12Z and
previous 00Z members of the HREF suite showed a relatively large
spread in location and magnitude of heavy rainfall but decent
agreement for at least 3 to 5 inches. Low confidence in location
resulted in a broadening of the previous Marginal RIsk area over Wisconsin/Illinois to include locations to the west, south and east.

...Northeastern Gulf Coast to Coastal Mid- Atlantic...

High moisture will remain across the Coastal Plain of the Carolinas
into the Florida Panhandle today into Friday morning, ahead of a
mid-level trough axis in place over the Southeast and an embedded
vorticity max forecast to move eastward from the southern
Appalachians. Precipitable water values are expected to remain near
2 inches along the coast and into northern Florida.

Thunderstorms will increase with daytime heating and low level flow
from the east to northeast will originate from the higher moisture
airmass. Scattered coverage of thunderstorms is expected across
portions of the Mid-Atlanitc and Southeast with cells exhibiting occasional slow movement and training. The high moisture and sufficient
instability (at least 500 to 1500 J/kg MLCAPE) will be capable of
producing 2 to 3+ in/hr rainfall rates at times, some of which
could fall on urban centers or locations with above average
rainfall over the past week.

Otto


Day 2
Valid 12Z Fri Aug 08 2025 - 12Z Sat Aug 09 2025

...THERE ARE MARGINAL RISK AREAS FOR EXCESSIVE RAINFALL ACROSS
PORTIONS OF THE NORTH-CENTRAL U.S. AND SOUTHEASTERN COAST INTO
NORTHERN FLORIDA...

...Northern Plains into Upper and Middle Mississippi Valley...

There is potential for a lingering MCS to be in place over
Minnesota at the start of the period (12Z Friday). The potent
closed low/upper trough from Thursday night will continue to
advance across the north-central U.S. on Friday/Friday night.
Thunderstorms, some possibly slow moving, are expected to impact
portions of northeastern Montana during the day on Friday while
thunderstorms expand in coverage during the afternoon over North
Dakota into portions of South Dakota. By 00Z Saturday, a cold front
is expected to become better defined over the Dakotas and move into
a fairly unstable and moist airmass from the eastern Dakotas into
Minnesota. Numerous thunderstorms are expected ahead of this
boundary for Friday night, with fairly progressive movement but
potential for training within a strengthening nocturnal low level
jet, out ahead of the front.

...Northeastern Gulf Coast to Coastal Mid-Atlantic...

Eastward movement of the mid-level trough over the Mid-Atlantic
states will allow the higher moisture along the coast to push
offshore but anomalous moisture will remain over Florida (1 to 2
standardized precipitable water anomalies). Sea breeze convergence
along the coast in the Southeast will allow for at least some
potential for flash flooding due to high rainfall rates from
thunderstorms with 2 to 3+ in/hr rates possible. Farther south, low
level easterly flow and a lingering surface boundary are expected
to focus convection from northern Florida into the western
Peninsula during peak heating hours. There will be spotty potential
for 3 to 5+ inch rainfall totals across the coast of the Carolinas
down into portions of northern Florida.

Otto


Day 3
Valid 12Z Sat Aug 09 2025 - 12Z Sun Aug 10 2025

...THERE ARE MARGINAL RISK AREAS FOR EXCESSIVE RAINFALL ACROSS
PORTIONS OF THE CENTRAL PLAINS INTO THE UPPER MIDWEST AND OVER THE
SOUTHWESTERN U.S...

...Upper Midwest...

A cold front will advance eastward into the Upper Mississippi
Valley on Saturday ahead of a strong mid-level trough moving across
the north-central U.S. Standardized precipitable water anomalies of
+2 to +3 are forecast by the 00Z GFS to be in place ahead of the
front over the Upper Mississippi Valley, supporting growing
instability with daytime heating. Unidirectional southwesterly flow
ahead of the front will allow for periods of training with
thunderstorms that form in the pre-frontal environment with
potential for multiple rounds of storms.

...Central Plains...

The cold front will move through the central Plains with low level
upslope flow in its wake over the High Plains region. Precipitable
water values are forecast to be near to slightly above average and
ascent will be aided by the region's placement within the
divergent and diffluent right- entrance region of the upper jet
located on the eastern side of the advancing upper trough axis.
Thunderstorms will likely shift east from eastern Colorado into
Kansas, meeting with an increasing low level jet of 40 to 50 kt
beyond 00Z Sunday. The 00Z model consensus is for an axis of
locally heavy rain stretching from eastern Colorado into Kansas and
southern Nebraska. Current thinking is for some 2 to 4 inch
rainfall totals, most of which could fall over a 2-3 hour window.

...Southwest...

Flow around a mid-level ridge centered over New Mexico should
prompt increasing moisture into the Southwest with precipitable
water values reaching near climatology for early August over
Arizona and New Mexico. Assuming a lack of widespread cloud cover
beneath the ridge should allow for sufficient CAPE generation by
mid-afternoon and typical monsoonal thunderstorm coverage by
evening. The concern for flash flooding will be enhanced by slow
storm motions given 00Z model forecasts of 850-300 mb mean wind
speeds of 10 kt or less.

Otto
$$
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FOUS30 KWBC 080908
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
508 AM EDT Fri Aug 8 2025

Day 1
Valid 12Z Fri Aug 08 2025 - 12Z Sat Aug 09 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER CENTRAL AND
NORTHERN MINNESOTA INTO FAR NORTHWESTERN WISCONSIN...

...Northern Plains through Upper Mississippi Valley...

An anomalous 500 mb low will track eastward from the
Montana/Canada border today with strong height falls moving into
the Dakotas later today and tonight. At the surface, low pressure
over South Dakota will track eastward toward Minnesota today before
advancing into southern Canada overnight as a cold front becomes
more defined to its south. Strong to extreme instability is
forecast again with this system today, ahead of the low/front over central/southern Minnesota along with highly anomalous moisture
over central and northern Minnesota (+2 to +4 standardized
anomalies via 00Z GFS). The front will steadily track eastward
between 00-12Z Saturday but potential will exist for high rainfall
rates given the environment.

An MCS from early Friday morning is expected to continue eastward
into the northern half of Minnesota early in the period but with a
weakening trend as the low level jet weakens and veers. While this
first round of rainfall is not expected to pose much in the way of
a flash flood threat prior to 18Z, high short term rates and
perhaps an inch or so of rain may prime soils for a second round
Friday night. A second round of thunderstorms is expected to form
over eastern North Dakota by late evening with convection
orienting from NNE to SSW with the advancing cold front. Numerous
thunderstorms are expected ahead of this boundary for Friday night
as low level forcing combines with increasing diffluence/divergence
aloft ahead of a jet max east of the upper low. Should line
orientation briefly match the mean steering flow, allowing for
training, high rain rates of perhaps 2+ in/hr can be realized as
the convective axis shifts eastward into northwestern Wisconsin by
Saturday morning. A Slight Risk was introduced for the potential
for flash flooding and potential for 2-4 inches in central to
northern Minnesota. The Marginal Risk surrounds this region for
lower confidence in excessive rainfall potential.

...Southeastern Coast into Northern and Central Florida...

High moisture with precipitable water values near 2 inches (a bit
higher over central/northern Florida) will be in place again today
in the vicinity of a lingering stationary front that extended from
offshore of the Carolinas into northern Florida. Daytime heating
should allow MLCAPE values to rise into roughly the 1000-2000 J/kg
range. Weak mid-level ridging over Florida will be accompanied by
weak deeper layer mean flow, supportive of slow storm motions. 00Z
models support the potential for some slightly stronger low level
flow over the western Peninsula, northeast of an inverted trough
axis in the eastern Gulf, which could increase potential for slow
cell movement/backbuilding. The environment could support rain
rates of 2 to 4 in/hr, but the threat appears rather isolated to
widely scattered, only supporting a Marginal Risk.

Otto


Day 2
Valid 12Z Sat Aug 09 2025 - 12Z Sun Aug 10 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER IOWA INTO
SOUTHERN WISCONSIN AND NORTHWESTERN ILLINOIS...

...Midwest...

A cold front will enter the upper Great Lakes to central Plains and
stall on Saturday as the core of an anomalous 500 mb low tracks
northeastward from south-central Canada. Precipitable water values
of 1.5 to 2.0 inches are forecast by the model consensus to pool
along the front and moderate to strong instability values are
likely to develop with daytime heating. While there may be some
lingering convective activity along the front Saturday morning
across the Upper Midwest, the main flash flood concern is expected
to develop later in the day on Saturday. Backing low level flow is
forecast to setup east of a surface low in Kansas with 30-40 kt at
850 mb forecast by the 00Z model consensus (some guidance is near
50 kt Saturday night). Flow aloft will be divergent and diffluent
to the south of an upper jet max over the upper Mississippi Valley,
enhanced by an upstream shortwave trough forecast to advance
through the central Rockies Saturday night. Increased forcing for
ascent along the front with mean steering flow parallel to the
synoptic front should favor areas of training with heavy rain
likely. While the details are a bit uncertain, the most likely
areas to see heavy rain potential (3 to 5 inches) will be near the
front from Iowa into southern Wisconsin and far northwestern
Illinois where a Slight Risk was introduced with this update.

...Central Plains...

In the wake of a cold front moving into the southern High Plains,
low level upslope into western Nebraska/Kansas and eastern Colorado
will favor increased moisture into the region and sustaining of
thunderstorms forecast to move off of the higher terrain by
Saturday afternoon. MLCAPE is forecast to be at least 1000-1500
J/kg over the High Plains and when combined with sufficient shear
aloft, some organized storms will be possible. There will be
potential for isolated flash flooding late Saturday evening into
the overnight as a low level jet develops, aiding convergence in
the vicinity of the frontal boundary, forecast to return north as a warm front.

...Southeastern Coast into Northern and Central Florida...

A similar setup across the Southeast will set up for Saturday as
was in place for Friday with high precipitable water values over 2
inches in place from the eastern Gulf coast into coastal South
Carolina near a lingering front. Portions of the outlooked area
will have weak steering flow in place yet again and low to mid-
level winds from the east to southeast will favor scattered
thunderstorms during peak heating with potential for brief training/backbuilding and high rates of 2-4 in/hr. At this time,
coverage of flash flood potential looks to be low enough to
warrant only a Marginal Risk.

...Southwest...

The mid to upper-level ridge that will be in place from Friday into
Saturday will begin to break down as upper level troughing
amplifies into the region from the north. Moisture values are
expected to return to near seasonal levels for early August across
Arizona while remaining slightly below average in New Mexico.
Thunderstorms are expected to form with solar insolation along the
higher terrain by 18Z, ramping up in intensity and coverage through
21Z. Given the increase in moisture compared to prior days, storms
should have a better shot of producing 1 to 2 in/hr rates,
especially across the southern half of Arizona and New Mexico where
weaker steering flow will be present as 00Z model forecasts show
850-300 mb mean wind speeds of 10 kt or less.

Otto


Day 3
Valid 12Z Sun Aug 10 2025 - 12Z Mon Aug 11 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER FROM EASTERN NEBRASKA/KANSAS INTO SOUTHERN WISCONSIN/NORTHERN ILLINOIS...

...Central Plains into Upper Midwest...

A quasi-stationary front will be in place from Sunday into Monday,
extending from the Great Lakes into the southern High Plains. The
base of an upper trough axis will be moving overhead through Monday
morning with southwesterly flow downstream along/over the front. An
enhanced low level flow regime will be in place much of the day
across the southern High Plains into the Midwest with potential
for mid-level impulses within the southwesterly flow aiding with
lift across the Plains to Midwest. The parallel nature of the
steering flow and frontal boundary will again favor the potential
for repeating and training of thunderstorms. Multiple rounds of
thunderstorms will be possible with peak flash flood potential
occurring late Sunday evening and overnight as convection moving
off of the higher terrain meets with strengthening low level flow
ahead of the upper trough. Precipitable water anomalies will
generally be +1 to +2 over the Plains with higher values toward the
Great Lakes. Questionable instability values over the Great Lakes
region will limit flash flood potential as the better consensus for
instability will be over southern locations. Model QPF values
seemed to agree with at least 3 to 5 inch potential from the global
guidance and locally higher from the 00Z RRFS and regional CMC.

...Southern Mid-Atlantic Coast to Northeastern Gulf Coast...

A lingering frontal boundary over northern Florida and high
pressure anchored over the northern Mid-Atlantic will maintain
low level southeasterly winds into the southeastern U.S. on Sunday. Precipitable water values of 2.0 to 2.3 inches over the Southeast
and Florida will again support intense tropical downpours as
thunderstorms increase with daytime heating. Low level
southeasterly winds and confluent axes will combine with sea breeze
convergence and other mesoscale boundaries to support scattered
thunderstorms with isolated flash flood potential from 2-4 in/hr
rainfall rates.

...Southwest...

Continued advancing of the base of an upper trough from the central
Rockies into the central Plains and an elongated ridge over
California will favor northwesterly mid-level flow into the
Southwest. While this may reduce moisture availability across the
Four Corners region, low level southerly flow is expected to be in
place over the northern Gulf of California into Arizona, with
westerly flow advecting low to mid-level moisture downstream toward
New Mexico. Meanwhile, the front over the High Plains from
Saturday night is forecast to again sink down to the south with an
upslope flow regime setting up over northeastern New Mexico,
helping to increase low level moisture into the region. Moisture
values for much of central/southern Arizona and New Mexico are
expected to be near average and monsoon thunderstorms are expected
during the late afternoon and evening hours with perhaps greater
coverage than previous days. Typical potential for high short term
rain rates (1-2 inches in an hour or less) will set up with
isolated to widely scattered flash flood potential.

Otto
$$
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FOUS30 KWBC 110823
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
423 AM EDT Mon Aug 11 2025

Day 1
Valid 12Z Mon Aug 11 2025 - 12Z Tue Aug 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHERN PLAINS, COASTAL NORTH AND SOUTH CAROLINA AND ACROSS THE FLORIDA...

...Southern Plains...
The active early morning convection currently across portions of
the Southern and Central Plains will likely weaken prior to or
shortly after 1200 UTC Monday. The latest hi res model consensus is
for the next round of convection to then form farther south along
the surface frontal boundary stretching from the Southern High
Plains, northeastward into the Lower MO Valley. No major changes
made to the previous slight risk area, with the current version
fitting well where both the HREF mean and RRFS mean neighborhood
probabilities for 1 and 2"+ amounts are high. PW values will remain
high, 1.5 to 2"+ in the slight risk area. This combined with
favorable upper difluence on the southeast side of the slow moving
mid to upper level trof moving across the Southern Plains, will
support potential for additional heavy precipitation totals. A
period of slow moving/training cells parallel to the frontal
boundary, primarily in the 0000 to 1200 UTC Tuesday period will
support localized hourly rainfall rates of 1"+.

No changes made to the marginal risk area extending farther to the
northeast into the Mid Mississippi Valley and Lower Lakes region.
The HREF and RRFS mean neighborhood probabilities are not as high
for 1 and 2"+ amounts as over the Southern Plains. Localized heavy
rainfall amounts along this portion of the front, are expected to
be to the south of where the heaviest rainfall fell over the past
24 hours from northeast IA, far northwest IL and southern WI. For
these reasons, the threat level was maintained as marginal.

...Northeastern Gulf Coast...
An axis of tropical PW values, 2 to 2.25"+, will push
northwestward in association with mid level shortwave energy moving
across the northeastern Gulf. Active showers likely in this high
PW axis along the immediate central to northeastern Gulf coastal
regions. HREF and RRFS mean neighborhood probabilities are high for
for 1, 2 and 3"+ totals from the Florida Panhandle, west across
far southern AL, far southern MS, southern LA into coastal
northeast TX. A slight risk was maintained across the FL Panhandle
region. The marginal risk was extended westward to cover the high
HREF and RRFS mean neighborhood probabilities across far southern
AL, far southern MS, far southern LA into coastal northeast TX.
There is consensus for potentially two periods of potentially
.50-1"+ hourly rainfall amounts during the day 1 period. The first
early this morning, extending into the post 12Z Monday period,
followed by another uptick in coastal precip intensities in the
early hours of Tuesday, 0600-1200 UTC.

...Coastal South and North Carolina...
The anomalous PW axis moving northwest into the immediate Gulf
Coast day 1 will also remain in place farther to the northeast
from GA into SC and NC. Only some small changes made to the
previous slight risk areas along the SC and NC coasts, extending
the slight risk approximately 50 miles farther northeast along the
NC coast to cover the latest model qpf and higher HREF/RRFS
probabilities. Active showers likely in this anomalous PW axis as
onshore south southeasterly flow persists day 1. There will be the
likelihood of training of precip areas in the south southeasterly
flow, supporting localized hourly rainfall totals of 1-2"+. The
marginal risk area over west central NC was extended approximately
50-100 miles to the north to cover the latest model qpf.

Oravec


Day 2
Valid 12Z Tue Aug 12 2025 - 12Z Wed Aug 13 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE LOWER
LAKES, SOUTHWESTWARD INTO THE MIDDLE MISSISSIPPI VALLEY AND INTO
THE SOUTHERN PLAINS, FROM THE CENTRAL GULF COAST INTO THE
CAROLINAS AND ACROSS PORTIONS OF THE SOUTHWEST...

...Lower Lakes into the Mid MS Valley and Southern Plains...
An axis of high PW values, 1.5-1.75"+ will continue along and ahead
of the elongated frontal zone stretching from the Lower Lakes,
southwestward into the Mid MS Valley and into the Southern Plains.
Scattered convection likely in this high PW axis, supporting
locally heavy precip totals. The previous marginal risk area was
extended farther southwestward from southern MO, across northwest
AR, much of OK and into northern TX to cover model qpf spread. Also
expanded the previous marginal risk area farther northwestward
into eastern WI and the northern portion of the L.P. of MI to cover
the model qpf spread for potentially locally heavy rainfall totals
along the northern portion of the frontal zone across these areas.

...Central Gulf Coast into the Carolinas...
The axis of high PW values stretching from the Central Gulf Coast
into the Carolinas on day 1 will persist across these regions day
2. Shortwave energy embedded in this high PW axis will continue to
support potential for additional heavy rains day 2. The previous
marginal risk area was extended east northeastward from northern
GA/Upstate of SC/far western NC to cover much of the remainder of
NC and SC where several models show heavy rain potential.

...Southwest...
No changes made to the previous marginal risk area from southeast
AZ into much of NM. Weak shortwaves progged to rotate around the
mid to upper level ridge building eastward into the Great Basin day
2, enhancing large scale uvvs in an axis of seasonable PW values.
Scattered convection across this area will support potential for
localized heavy rainfall amounts and isolated runoff issues,
especially across more vulnerable terrain features or burn scars.

Oravec


Day 3
Valid 12Z Wed Aug 13 2025 - 12Z Thu Aug 14 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE LOWER
MISSISSIPPI VALLEY INTO THE TENNESSEE AND OHIO VALLEY AND EASTERN
LAKES, ACROSS COASTAL SOUTH CAROLINA AND COASTAL NORTH CAROLINA,
PORTIONS OF THE NORTHERN PLAINS AND OVER THE SOUTHWEST...

Similar to the day 2 period, an axis of high PW values will
continue to stretch from the Central Gulf coast, east northeastward
into the Southeast and Southern Mid Atlantic. Widespread scattered
convection likely in this anomalous PW axis, values 1.5-2 standard
deviations above the mean. Mid to upper level dynamics will have
weakened by day 3, with less defined areas of upper diffluence to
accentuate lift in this high PW axis. Still, model consensus is for
continued potential for continued locally heavy rains across these
areas. A marginal risk was added for the upper coast of SC and the
lower coast of NC where models do show potential for additional
locally heavy rains day 3.

...Lower Lakes/Northeast into the OH/TN Valley, Central to
Southern Appalachians...
An axis of high PW values, 1.5-1.75"+ also likely to continue
along the elongated frontal zone pushing eastward through the Lower
Lakes into NY State and northern New England and stretching
southwestward into the OH/TN Valley regions and Central to Southern Appalachians. Widespread scattered convection likely along this
front in this high PW axis, supporting locally heavy rains and
isolated runoff issues. No changes made to the previous marginal
risk area along and ahead of this front.

...Southwest...
No significant changes to the overall flow pattern for the
Southwest day 3. Additional weak vorts rotating around the Great Basin/Southwest mid to upper high will support another round of
scattered convection. Low confidence on any qpf details, but
potential will continue for localized heavy rains and isolated
runoff issues, especially across more vulnerable terrain features or burn scars.

...Northern Plains...
The low level southerly flow expected to strengthen after 0000 UTC
Thursday across the Northern Plains ahead of a surface front
emerging into the Northern Plains. An area of organized convection
possible ahead of this front, with locally heavy precip totals
possible. There is a lot of model spread with qpf details at the
moment, leading to low confidence. The previous marginal risk area
was decreased in size to better fit the overlap of potentially
heavy rains with the lower FFG values.

Oravec
$$
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FOUS30 KWBC 120828
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
428 AM EDT Tue Aug 12 2025

Day 1
Valid 12Z Tue Aug 12 2025 - 12Z Wed Aug 13 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHERN APPALACHIANS AND PORTIONS OF THE CENTRAL GULF COAST...

...SOUTHERN APPALACHIANS...
There continues to be a strong model signal for heavy rains in the
vicinity of the Southern Appalachians day 1. PW values remain well
above average from the Central Gulf coast, northeastward into the
Southern Appalachians and then eastward through the Carolinas and
Southern Mid-Atlantic. Convection will be enhanced through this
anomalous PW axis by a stream of mid to upper level vorts forecasts
to rotate across this region, around the peripheries of a weak mid
to upper level ridge centered just off the northeast Florida
coast. While locally heavy rains are possible anywhere in this high
PW axis, one strong model signal is across the Southern
Appalachians where moist upslope flow and enhanced uvvs from the
embedded vorts will support heavy precip. The slight risk area was
not changed much from the previous issuance and fits well with the
latest axis of high neighborhood probabilities from the HREF and
RRFS mean for 2"+ amounts. The RRFS mean has a more defined 3"+
high probabilities than the HREF, but both mean still emphasize the
area in the vicinity of the Southern Appalachians for heavy rains day 1.

...Central Gulf Coast...
A slight risk was continued along portions of the Central Gulf
Coast from in the vicinity of Pensacola, west to New Orleans.
Consensus from the latest hi res guidance is for the potential for
two periods of heavy rains affecting the immediate coastal region
in association with the mid level vorts rotating north
northeastward off the Gulf. HREF probabilities for .50 to 1"+
amounts begin to increase prior to 1200 UTC Tuesday and continue to
be high until 1500 UTC across the Central Gulf coast. A second
period of high hourly HREF probabilities for .50-1"+ then occurs
again in the early hours of Wednesday, beginning around 0600 UTC
and continuing to just after 1200 UTC. Isolated runoff issues
possible from each heavy precip max period, especially in more
urbanized regions.

...Great Lakes, Ohio Valley, Mid Mississippi Valley into the
Southern Plains...
A broad marginal risk area was maintained across a large region
from the Great Lakes, south and southwestward into the OH Valley,
Mid MS Valley and Southern Plains. PW values will remain high
across these regions, 1.5 to 2"+, with the latest suite of models
showing at least localized heavy rain potential in this high PW
axis. While HREF and RRFS neighborhood probabilities for 1"+ totals
are high across these areas, the probabilities do drop
significantly for higher totals. The HREF EAS probabilities for 1"+
are low across much of this region, depicting poor overlap with
the hi res heavy rain areas. One exception is over northeast IL
into far northern IN and southwest L.P. of MI where EAS 1"+
probabilities are as high as 25-30%, showing better hi res heavy
rain overlap. The higher EAS probabilities are to the southeast of
where the heaviest rains have occurred recently. This and the
expected progressive nature of the convection, supports keeping
the risk level as marginal.

...Southwest...
No changes made to the previous marginal risk area from southeast
AZ into much of NM. Weak shortwaves progged to rotate around the
mid to upper level ridge building eastward into the Great Basin day
1, enhancing large scale uvvs in an axis of seasonable PW values.
Scattered convection across this area will support potential for
localized heavy rainfall amounts and isolated runoff issues,
especially across more vulnerable terrain features or burn scars.

Oravec


Day 2
Valid 12Z Wed Aug 13 2025 - 12Z Thu Aug 14 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF
THE EASTERN AND SOUTHERN UNITED STATES, AS WELL AS FOR PORTIONS OF
THE NORTHERN PLAINS AND SOUTHWEST...

No changes of note made to the very broad marginal risk area day 2
stretching northeastward from the Central Gulf coast, into the
TN/OH Valleys, Southern to Central Appalachians, Mid-Atlantic into
NY State and northern New England. A broad axis of above average PW
values, 1.5 to 2+ standard deviations above the mean will stretch
along and ahead of the primary surface front moving west to east
across the northern tier from the Lower Lakes/OH Valley region,
east into the Mid-Atlantic/Northeast. The above average PW values
across the Gulf coast into the Southeast/Southern Mid-Atlantic
during day 1, will also continue into day 2. There is general
agreement in the models for the potential for widespread scattered
convection in this high PW axis, with areal average moderate totals
depicted and likelihood of locally heavy totals. Confidence is low
with respect to where the heavier, more concentrated convection may
be. Subsequently, we have not changed the risk level from previous
issuances, maintaining it at marginal for the time being.

A few areas of concern for potential higher threat level day 2 in
subsequent issuances.

Southern Appalachians: Early morning heavy rains late day 1 across
the Southern Appalachians may linger into the post 1200 UTC
Wednesday period across eastern TN/western NC. The HREF 12 hour
neighborhood probabilities ending 0000 UTC Thu Aug 14 are high for
1 and 2"+ amounts.

Mid-Atlantic: Convection likely to begin to become more organized
ahead of the above mentioned frontal boundary pushing eastward.
HREF 12 hour neighborhood probabilities ending 0000 UTC Thu Aug 14
are high for 1 and 2"+ amounts from northern VA, northward across
much of PA into the Southern Tier of NY State.

Central Gulf Coast: HREF hourly precip probabilities for .50-1"+
amounts remain high early day 2 from the expected second round of
heavy rains to affect the Central Gulf coastal region during the
day 1 period, that may extend into the day 2 period.

...Northern Plains...
There continues to be a lot of model spread day 2 with potential
convective development ahead of the next front pushing into the
Northern High Plains 0000-1200 UTC Thursday. The low level
southerly flow expected to strengthen after 0000 UTC Thursday
across the Northern Plains ahead this front, supporting increasing
convective potential. Several of the global models do show
potential for heavy amounts late day 2, but continue to show large
amounts of spread with respect to placement, leading to continued
low confidence. Given this, the risk level was maintained at marginal.

...Southwest...
No significant changes to the overall flow pattern for the
Southwest day 2. Additional weak vorts rotating around the Great Basin/Southwest mid to upper high will support another round of
scattered convection. Low confidence on any qpf details, but
potential will continue for localized heavy rains and isolated
runoff issues, especially across more vulnerable terrain features
or burn scars.


Day 3
Valid 12Z Thu Aug 14 2025 - 12Z Fri Aug 15 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE LOWER
MISSISSIPPI VALLEY, TENNESSEE VALLEY, SOUTHERN APPALACHIANS INTO
THE SOUTHEAST AND ACROSS THE SOUTHWEST AND THE UPPER MISSISSIPPI VALLEY...

...Southeastern portion of the CONUS...
The cold front moving across the northeast tier of the CONUS day 2
will keep the axis of above average PW values, 1.5 to 2+ standard
deviations above the mean, concentrated across the southeast
quarter of the CONUS from the Lower MS Valley, east across the TN
Valley, Southern Appalachians and into the Southeast. There is
general model consensus for widespread scattered convection across
these areas day 3, with locally heavy rains likely where convection
becomes more organized. Large scale uvvs will continue to be
enhanced by shortwaves rotating around the mid to upper level ridge
that is expected to build westward day 3 across North Florida into
the northeast Gulf. Models are showing a lot of spread with qpf
details day 3, keeping the risk level, at the moment to marginal
across these areas.

...Southwest...
Similar to the day 2 period, no significant changes to the overall
flow pattern for the Southwest expected on day 3. Additional weak
vorts rotating around the Great Basin/Southwest mid to upper high
will support another round of scattered convection. Low confidence
on any qpf details, but potential will continue for localized heavy
rains and isolated runoff issues, especially across more
vulnerable terrain features or burn scars.

..Upper Mississippi Valley...
The frontal boundary moving into the Northern Plains day 2 will
continue to push eastward into the Upper MS Valley day 3. There may
be two rounds of precip affecting this area day 3. An initial
surge of warm advection rains early day 3, followed by potential
frontal convection late day 3. Continued low confidence in any qpf
details at this range, warranting only a marginal risk.

Oravec
$$
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FOUS30 KWBC 131251
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
851 AM EDT Wed Aug 13 2025

Day 1 Valid 1244Z Wed Aug 13 2025 - 12Z Thu Aug 14 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE SOUTHERN
AND CENTRAL APPALACHIANS...NORTH TEXAS AND THE IMMEDIATE CENTRAL
GULF COAST...

1245Z Excessive Rainfall Discussion...
Issued a special Excessive Rainfall Outlook to hoist Slight Risks
in the northern portion of Texas where convection has been growing
upscale in intensity and areal coverage. Latest short-range
CAM guidance showed some 3 to 5 inch rainfall potential here which
seems consistent given the potential for some back-building
convection. Refer to WPC Mesoscale Precipitation Discussion 924.
Also introduced a Slight Risk area along the Gulf coast...mainly
over the Florida peninsula...where an area of showers and
thunderstorms has been dropping locally intense downpours.
Additional details in the WPC Mesoscale Precipitation Discussion
923. Only other change was to extend the pre-existing Slight Risk
in the Central and Southern Appalachians southwestward into parts
of southern Tennessee and northern Alabama based on latest trends
in radar imagery.

Bann

...Southern Appalachians...

A cold front over the Great Lakes to mid-Mississippi Valley early
Wednesday morning is forecast to advance southeastward into New
York, the central Appalachians and western Kentucky/Tennessee by
Thursday morning. High moisture with precipitable water (PW)
anomalies of 1 to 2+ are forecast to extend ahead of the cold front
from central Texas to western New England and much of the East
Coast. Across the southern Appalachians, there may be an early
round of locally heavy rainfall early Wednesday, related to
lingering nocturnal convection. The greater concern will be later
today with peak afternoon heating and scattered coverage of
thunderstorms, ahead of a synoptic scale mid-level trough axis
approaching from the northwest and a low to mid- level impulse
tracking around a ridge offshore of the Southeast, with some
locally enhanced southerly flow into the Appalachians. 00Z HREF and
18Z REFS neighborhood probabilities of exceeding flash flood
guidance (FFG) were a bit higher here than other areas of the U.S.
with potential for some 2-4 inch totals (locally higher) through
Thursday morning.

...Remainder of Eastern U.S. into Lower Mississippi Valley...
Confluent and locally stronger 925-850 mb winds of 20-30 kt are
expected across Virginia/North Carolina as the region sits between
ridging to the south and troughing to the north today. There will
be some enhanced potential for training and backbuilding cells in
the west to east flow, coupled with PWs over 2 inches, supporting
potential for a few 3 to 5 inch totals.

Back toward Texas and much of the Lower Mississippi Valley, high
PWs and slow storm motions could support some widely scattered
instances of flash flooding during peak heating, with dissipation
into the overnight.

...Northern Plains...
A few thunderstorms will be possible over South Dakota in the
first 6 to 9 hours of the period, ahead of an advancing mid-level
impulse tracking eastward from southeastern Montana. Nocturnal
strengthening of the low level jet is expected overnight, ahead of
a shortwave approaching from the west, with southerly winds of 35
to 45 kt at 850 mb forecast by the 00Z GFS through the central
Plains into the Dakotas. A small MCS is possible near a warm front
across the region overnight but details on exact location and
rainfall totals remain a bit uncertain. The Marginal Risk covers
the probabilities for 2+ inches highlighted in the 00Z HREF and 18Z REFS.

...Southwest...
A ridge aloft over the Four Corners region is forecast to slowly
shift east into eastern New Mexico by Thursday morning, ahead of an
approaching upper trough into California. Some increase in PWs are
expected into Arizona and southwestern New Mexico during the period
but values will climb to near average by 00Z Thursday. An
expectation of decent solar insolation with limited cloud cover
should support seasonable instability values into the region for
this afternoon/evening and Localized flash flooding will be
possible with diurnally driven thunderstorms, especially across
more vulnerable terrain features or burn scars.

Otto


Day 2 Valid 12Z Thu Aug 14 2025 - 12Z Fri Aug 15 2025

...THERE ARE MARGINAL RISKS OF EXCESSIVE RAINFALL FROM THE LOWER
MISSISSIPPI VALLEY TO THE MID-ATLANITC COAST AND NORTHEAST...AS
WELL AS THE SOUTHWEST AND THE UPPER MISSISSIPPI VALLEY...

...East Coast to Lower Mississippi Valley...
The cold front from Wednesday will continue to advance toward the
southeast with lingering high moisture ahead of the boundary from
New England into the Mid-Atlantic Coast. Potential for localized
excessive rainfall within the anomalous PW axis and with forcing
ahead of the front, but cloud cover may limit the potential for
higher instability values. There should be at least an isolated
flash flood threat with thunderstorms ahead of the front from
southern New England to the Mid-Atlantic coast.

Farther south, from the Southeast to the Lower Mississippi Valley,
there does not appear to be a substantial focus area for excessive
rainfall potential, hence the broad Marginal Risk, but high
moisture and daytime heating will result in scattered thunderstorms
with peak rainfall rates in the 1 to 3 in/hr range. Similar to
Wednesday, parts of the Lower Mississippi Valley will have high PWs
and slow cell motions given placement between a mid- level ridge
center over KS and another over the northeastern Gulf.

...Southwest...
The upper trough over California on Wednesday will continue to move
east on Thursday with increased moisture advection into Arizona and
parts of Utah into the Four Corners region. PW values are forecast
to increase to near +1 standardized anomaly for Arizona into
southern Utah. While cloud cover is a bit uncertain for Thursday
into Friday, ahead of the western trough and from any lingering
disturbances from the previous day, A similar sized, perhaps
slightly larger, Marginal Risk is drawn for Thursday into Friday
following the model QPF consensus and Arizona Regional WRF
simulated reflectivity, which showed the potential for more
widespread coverage of thunderstorms on Thursday compared to Wednesday.

..Upper Mississippi Valley...
A cold front will move into the north-central U.S. on Thursday with
a steady enhancement to southerly/southwesterly 850 mb winds ahead
of the boundary. Even after diurnal weakening of the nocturnal low
level jet, 00Z GFS forecasts show 20-40 kt continuing from the
central Plains into the eastern Dakotas and Minnesota through
Thursday evening. Locally heavy rain may be ongoing Thursday
morning with decent potential for another round Thursday night with
favorable jet diffluence/divergence aloft, possible moderate
instability and standardized PW anomalies of +1 to +2. Confidence
on the exact location remains uncertain however, with hopefully
increasing confidence occurring as we move into the hires range.

Otto


Day 3 Valid 12Z Fri Aug 15 2025 - 12Z Sat Aug 16 2025

...THERE ARE MARGINAL RISKS OF EXCESSIVE RAINFALL FROM THE LOWER
MISSISSIPPI VALLEY TO THE SOUTHEAST COAST...AS WELL AS THE
SOUTHWEST/FOUR CORNERS REGION AND THE UPPER MISSISSIPPI VALLEY...

...Southeast Coast to Lower Mississippi Valley...

Lingering high moisture will be in place on Friday, south of a
southward sagging frontal boundary with standardized PW anomalies
of +1 to +2 from the Lower Mississippi Valley to the Southeast
Coast. With an upper ridge centered over the northeastern Gulf,
there will be potential for mesoscale impulses to ridge around the
ridge and help focus diurnally driven thunderstorms during peak
heating. Similar to previous days, locally high rain rates with 1
to 3 in/hr may occur with localized training.

...Upper Mississippi Valley...
A cold front will continue to advance downstream through the Upper
Mississippi Valley but slow/stall back toward the west. PWs will
remain above average in the vicinity of the front and organized
thunderstorm potential will exist within the mean westerly flow
aloft. Similar to previous days, nocturnal strengthening of the low
level jet at night will have the potential to generate an MCS or loosely-organized convective cluster with localized training
potential. Confidence is rather low at 3 days out, but the Marginal
Risk was drawn to cover the various model solutions and conceptual
thinking for greatest rainfall potential near the front and low
level jet axis intersection.

...Southwest...
Active southwesterly flow across much of the western U.S. will
encourage the further expansion of above average moisture into the
Four Corners region and northern Great Basin. While standardized PW
anomalies will generally peak in the +1 to +2 range, not everyone
within these anomalies will see the same flash flood potential. The
focus appears to be best tied to the Mogollon Rim into the Wasatch
and central to southern Rockies, ahead of a number of shortwave
impulses moving in from southern California. Tied to the relatively
stronger belt of westerlies could be jet-induced divergence maxima
aloft to help in the production of locally heavy rainfall.

Otto
$$
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FOUS30 KWBC 162005
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
405 PM EDT Sat Aug 16 2025

Day 1
Valid 16Z Sat Aug 16 2025 - 12Z Sun Aug 17 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER MIDWEST AND A SMALL PORTION OF SOUTHERN NEW MEXICO...

...Upper Midwest and Northern Plains...

Small changes were made to the outlook to adjust for observational
trends; the most consequential was a slight southward shift in the
Slight Risk area in the Upper Midwest. The latest radar trends
suggest a compact MCS in C WI will continue to progress east-
southeast or southeast late this morning and early this afternoon,
with potential for some training of higher rain rates on the
upshear flank of the cold pool. However, greater concern for
backbuilding and training convection would be for convective
development expected to occur later -- generally near the
instability gradient. However, hi-res model guidance (even runs
initialized at 12Z) does not seem to have the best handle on the
ongoing situation across N/C WI, and this poses some challenges
with placing the most likely area for heavier rainfall. If the
ongoing MCS continues to expand southwest with additional
development on the upshear flank, and remain forward-propagating,
the outflow boundary could push further south than anticipated and
set up from N IL back toward NE IA. However, if the MCS remains
close to its current dimensions and upstream convection struggles
to become established in the next few hours, the outflow and
effective front would be more likely to be situated further north,
from S WI into SE MN. These differences are crucial.

The overall pattern does support training and backbuilding with any
later rounds of convection developing along the instability
gradient. The nose of the LLJ will be focused back to the west,
with a large reservoir of strong instability, and a corridor of
deep, anomalously high moisture in place. Although hi-res models
are struggling to place things consistently at the moment, they all
generally show an overnight round of convection that backbuilds in
a nearly-stationary fashion, and this is consistent with the
conceptual model for this type of pattern. That scenario can
produce more significant impacts if realized, and so a Moderate
Risk upgrade was considered. However, given the lack of consistency
in guidance and uncertainties around ongoing convection, the Slight
Risk was maintained for now. We will be monitoring convective trends
over the next few hours for a possible unscheduled outlook update
this afternoon and a targeted upgrade to Moderate Risk.

...South-Central Texas, Along Gulf Coast and Southeast...

Very few changes were made to the outlook along the Gulf Coast
region, other than to remove the Slight Risk in C TX, which was
also coordinated with WFO EWX. The ongoing convection this morning
is very isolated and models have backed off on the heavy rainfall
signal in Texas in general. Nevertheless, the Marginal Risk was
maintained in these areas. A Slight Risk was also considered from
southeast Georgia into northeast Florida where 12Z HREF
probabilities of 2-4 inches of rain area most elevated and
concentrated. However, simulated reflectivity from the 12Z hi-res
members suggests that localized rainfall maxima would be most
likely through cell mergers and boundary collisions that would
briefly maximize rainfall in a certain area, rather than anything
lingering for several hours. Given the transient nature of the
heavy rainfall, we opted to maintain the Marginal Risk for now.

A Marginal Risk was also briefly considered for portions of the
Mid-Atlantic from far N VA into W MD, C/NE PA, and S NY. Isolated
convection has already developed and is not moving very quickly.
However, 12Z soundings show a significant amount of dry air aloft
and precipitable water values, although somewhat elevated, are not
highly anomalous. Therefore, any heavy rainfall and resulting flash
flooding would be expected to be fairly isolated. In other words,
the probability is non-zero, but less than 5% (Marginal Risk).

...Southwest...

Monsoonal moisture plume should focus farther east today,
shifting the potential for isolated flash flooding across
southeastern Arizona, and portions of southern New Mexico. CAMs
continue to support more concentrated activity in the Sacramento
Mountains, but have backed off on instability and rainfall
potential in southwest New Mexico. Therefore, the Slight Risk was
trimmed to be concentrated near the Sacramento Mountains
specifically. Another area of focus would be the Trans-Pecos and
Big Bend region of Texas, where 12Z HREF probabilities of 2 inch
rainfall are higher. There is a weakness in the mid-upper level
flow over this area, so developing thunderstorms have the potential
to be nearly stationary. It will be monitored for a potential
Slight Risk upgrade.

...Northwest and Northern Rockies...

Marginal risk remains across far north-central California and much
of central/eastern Oregon with an expansion across northern ID and
western MT. Elevated moisture from the record high moisture
atmospheric river (Salem OR had its highest PW on record at 00Z)
develops into a ribbon across these areas during peak heating today
which should produce isolated flash flood threats. Some of the
heavy rainfall could occur atop burn scars, locally enhancing
runoff potential.

Lamers/Jackson


Day 2
Valid 12Z Sun Aug 17 2025 - 12Z Mon Aug 18 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR A PORTION OF THE
UPPER MIDWEST...

...Upper Midwest...

A backbuilding band of thunderstorms may be ongoing at the
beginning of the period (12Z Sunday), however there is considerable uncertainty. The latest hi-res model guidance suggests this would
be most likely from S MN into SW WI, but there is placement
uncertainty related to the mesoscale evolution and outflow
boundaries over the next 12-18 hours, and uncertainty around how
well convection will be able to sustain itself. Models fairly
consistently show warming mid-level temperatures Saturday Night in
the same area. This generally reduces the size of the CAPE profile
during a critical time of convective initiation, and could increase
the strength of a cap.

However, if thunderstorm activity becomes more organized, the
overall pattern is favorable for training and backbuilding, with
the nose of a LLJ pointed into S MN, and an instability maximum
centered just to the southwest (upstream) of the most likely area
for convective initiation. Organized clusters of storms training in
a region of strong instability and anomalously high PWs could lead
to rapid accumulation of rain in a narrow corridor. Rain rates may
reach 2 inches per hour in that scenario, and thus there is a
conditional threat for some significant flash flooding. Given the
uncertainties expressed above, the overall categorical risk is
being held at Slight for now.

Additional thunderstorm development is expected late in the
afternoon or early in the evening on Sunday in eastern South Dakota
(or adjacent areas), and a continuation of strong instability and
anomalously high PWs would support high rain rates and a continued
flash flood threat overnight in the Slight Risk area.

...Elsewhere in the Country...

Multiple other Marginal Risk areas have been maintained -- from
Montana into the Dakotas, in portions of New Mexico and West Texas,
and in portions of Florida and southeast Georgia. A Marginal Risk
area was also added in the Mid Atlantic for Pennsylvania and
adjacent portions of neighboring states.

The common factor for all these areas is that, although there is
some risk of flash flooding, any higher rainfall rates and
thunderstorm activity should be relatively brief, and therefore
impacts should be relatively isolated.

Lamers


Day 3
Valid 12Z Mon Aug 18 2025 - 12Z Tue Aug 19 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR SOUTHERN NEW
MEXICO AND FAR WEST TEXAS, AND THE GREAT LAKES...

Confidence is lower in concentrated areas of excessive rainfall
and flash flooding for the Day 3 period, and thus the previous
Marginal Risk areas have largely been maintained. The Western Great
Lakes and the New Mexico and West Texas regions both are projected
to have precipitable water values near or above the 90th
percentile, and abundant instability. Therefore, even though the
details are unclear, the environment in each area is broadly
supportive of organized convection with high rain rates above 1
inch per hour at times. A future Slight Risk upgrade seems most
likely in the Great Lakes region due to much stronger low-mid level
inflow, supported by anomalously high integrated vapor transport
(above the 90th percentile based on the ECMWF ensemble mean).

Lamers
$$
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FOUS30 KWBC 170849
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
449 AM EDT Sun Aug 17 2025

Day 1
Valid 12Z Sun Aug 17 2025 - 12Z Mon Aug 18 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR A PORTION OF THE
UPPER MIDWEST...

...Northern Plains, Upper Midwest and Ohio Valley through Northern Mid-Atlantic...
Ongoing swath of repeating heavy rain from southern Minnesota
through Chicago and northern Indiana should diminish a fair amount
by 12Z. However, the remnant boundary should be a focus for
convection to fire upon later today over similar areas and
downstream over the Ohio Valley. This warrants a corridor of
Marginal Risk that connects the previous one over NY State.

Yet another MCS is tracking east through South Dakota tonight with
this one taking a bit of a northern track compared to the one last
night. This organized activity can be expected to be moving east
from the central Dakota border by 12Z with further afternoon
development over much of eastern Minnesota into Wisconsin with the
aid of the boundary lifting/pivoting from southern MN. Then, this
evening another round of organized heavy rain works its way across
much of MN reaching northern IA and southwest WI overnight. This
warrants northward expansion of the Slight Risk up to Duluth and
over more of western Wisconsin.

Farther east, scattered heavy thunderstorms over southern Ontario
are continuing to push east overnight with a cold front. Strong
moisture advection overnight ahead of the front is allowing for
much above normal moisture to spread over the eastern Great Lakes
with potential for 2" PW in the 12Z BUF raob. Morning heavy rain
works its way over western NY and much of PA where a Marginal Risk
remains. Stronger NWly flow around the central CONUS upper ridge
should keep activity fairly progressive, but the NWly flow did
warrant some expansion to the Marginal for the western slopes of
the central Appalachians.

Remnant moisture over Montana from the atmospheric river that
pushed into the Northwest a couple days ago could cause repeating
heavy enough rain to be excessive, so the Marginal Risk is
maintained there.

...New Mexico and Western Texas...
Continued east shift in the monsoonal moisture plume places an
isolated flash flood risk over eastern NM and far western TX into
the TX Panhandle today where the PW anomaly remains 1.5 sigma above
normal.

...Florida...
Persistent boundary over the northern FL Peninsula maintains high
moisture with 2.25" PW (2 sigma above normal). Mainly diurnally
driven convective activity may produce locally excessive rainfall
even with the high FFG (around 4"/3hr).

Jackson


Day 2
Valid 12Z Mon Aug 18 2025 - 12Z Tue Aug 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR SOUTHERN
WISCONSIN INTO NORTHERN ILLINOIS...

...Upper Midwest/Great Lakes...
Ongoing Monday morning convection is progged by the 06Z HRRR to be
over northeastern IA and southern WI to the IL border before
diminishing by midday. The remnant boundary then allows further
activity to fire over similar areas later that afternoon. Moisture
is quite elevated with PW peaking around 2" in the afternoon. The
overlap of these repeating rounds of heavy storms over already
saturated ground warrants an upgrade to a Slight Risk for much of
southern WI into northern IL per coordination with WFOs MKX and
ARX. Given the mesoscale processes over the persistent frontal
pattern generous coverage of the Marginal Risk is used to cover
much of the Midwest.

...Southwest...
The upper ridge axis shifts west to NM on Monday suppressing the
monsoonal flow and warranting a Marginal Risk over southern NM and
far western Texas.

...Southeast...
Added Marginal Risks over the southern Appalachians/Piedmont and
northern FL Peninsula for pooled moisture anomalies and perhaps
some remnant frontal boundary in FL. These areas would see
mainly diurnally driven convection.

Jackson


Day 3
Valid 12Z Tue Aug 19 2025 - 12Z Wed Aug 20 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE SOUTH
CENTRAL GREAT PLAINS THROUGH EASTERN MIDWEST AND IN THE SOUTHWEST...

...Central Plains to the Midwest...
Westward motion to the upper ridge axis allows the frontal wave
pattern over the Upper Midwest to finally eject southeast Monday
night. Positive moisture anomaly with PW 1.5 to 2 sigma above
normal extend from MI through MO by Tuesday afternoon. Frontal
forcing should allow for progressive motion, but activity could be
heavy enough to warrant an isolated flash flood risk and a Marginal
Risk. The 00Z global model consensus is for rainfall focus farther
west than previous runs, particularly for the EC. Therefore, in
coordination with WFOs BTV ALY BUF and BGM, the Marginal Risk was
trimmed out of the Northeast.

...Southwest...
Remnant moisture with PW anomalies around 1 sigma above normal are
over eastern AZ/much of NM on Tuesday. An isolated terrain driven
flash flood risk is possible in the diurnal convection, so the
Marginal Risk is maintained.

Jackson
$$
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FOUS30 KWBC 180723
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
323 AM EDT Mon Aug 18 2025

Day 1 Valid 12Z Mon Aug 18 2025 - 12Z Tue Aug 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
UPPER MIDWEST AND WESTERN GREAT LAKES...

...Upper Midwest/Great Lakes...

Radar/sat composite indicates a large expanse of convection
migrating to the east-northeast stemming from broad regional
forcing aided by a stout shortwave exiting out of the Northern
Plains. Current setup is progged to maneuver downstream into
WI/Northern IL with a elevated risk of heavy rainfall bisecting
area along and east of the I90/39 corridor. 00z HREF blended mean
QPF distribution focuses the heaviest rain across the
Milwaukee/Chicago metros with an expansion west back towards that
I90/39 interchange. This is consistent with the sharp theta_E
gradient oriented along the approaching warm front from the
southwest as we move through the morning hrs today. The boundary
referenced will be the suitable focal point for redevelopment as we
move beyond 16-18z as environmental conditions remain ripe for
enhanced convective initiation as conditions destabilize within the
broad warm sector along and south of the warm front. HREF probs
for >3" locally are running highest between Madison to Milwaukee
down into the northern periphery of IL, including the northern
suburbs of Chicago. This area is most prone to flash flood risks
due to the urbanization factors, as well primed soils from several
periods of heavy rainfall prior to what will transpire today. The
combination of the above factors lent credence to continuing the
SLGT risk inherited with some modest expansion on the northern and
southern periphery to account for trends in heavier QPF placement
down through IL and up into central WI.

...Front Range through Central Plains...

Series of convective complexes will migrate across the region
extending from the CO Front Range across the KS/NE line until it
reaches towards the Missouri River valley near northwestern MO.
Models are a bit all over the place on exactly how the setup
evolves downstream, but the consensus on initiation across the
Front Range and along the KS/NE border was enough to warrant
coverage with a MRGL risk as cells could produce rates >2"/hr when
assessing hourly prob fields from the HREF and individual CAM
outputs. Highest probs for >2" of rainfall are across northeast CO,
northwest KS, and the MO/KS/NE border with some of the CAMs
indicating upwards of 4" in either location. If consensus grows in
either location for >3", there's a chance for a targeted upgrade in
future updates. For now, the MRGL risk was sufficient.

...Southwest into Southern Plains...

Monsoonal moisture trapped under the ridge across NM/Southern
Plains will continue the persistent threat of scattered to
widespread convective development from southeast AZ up through
much of NM, west TX, and western OK. The scattered nature of the
convection and no real organized zone of precip will limit the
higher end potential for any risk, however the threat is certainly
within the bounds of a MRGL risk considering the threat for 2-3"
locally in any one location is forecast. The greatest threat will
likely situate over the Sacramento's thanks to the remnant burn
scar presence that enhances flash flood and debris flow concerns
locally in southern NM.

...Central Gulf Coast...

Very little change in the forecast for Monday. An easterly wave is
expected to traverse areas of central Gulf coast, leading to heavy
rainfall later this afternoon. PWATs generally >2" coupled with
sufficient buoyancy/instability running between 2500-4000 J/kg
MUCAPE will be plentiful for heavy convective cores capable of
rates between 2-4"/hr in the strongest cells. HREF neighborhood
probs for >3" are running between 30-45% near and south of I-10
with the best threats likely in the urban corridors from New
Orleans across into Lafayette to Lake Charles. The progressive
nature of the precip should alleviate the worst flash flood
concerns, but still remains within the lower end of the MRGL
threshold for the threat. Maintained general continuity from
previous forecast with some minor trimming of the eastern extent of
the risk area to remove southern MS.

...Mid Atlantic and Carolina's...

Prevailing east to northeast flow from the Lower Delmarva down
through the Carolina's will aid in enhancing regional convergence
along a southward advancing front stemming from low-level wedge
pattern as high pressure drills southward to the east of the Blue
Ridge. Theta_E maxima is generally confined to the VA Tidewater
down through eastern NC with a slope back west as you get into SC.
Models are relatively solid agreement on the placement of the
heaviest precip in these zones mainly due to the instability
presence promoting general convective schemes compared to more
low-topped showers and stratiform in the stable layer behind the
cold front. MRGL risk was last forecast was maintained with some
adjustments based on the latest QPF trends in the hi-res suite and
ensemble bias corrected output.

...Florida...

Seasonal PWATs and convergence of the sea breeze anticipated across
central FL will lead to a period of heavy rainfall along the I-75
corridor, including threats to the Orlando metro area. CAMs are
consistent on a zone of 3-6" locally the evolution across the above
area. This is a generally localized concern as is customary with
these setups, so the previous MRGL risk was kept with removal of
the eastern side of the state as the convergence zone will likely
occur too far west to generate much of a significant rainfall risk
in the I-95 corridor.

Kleebauer


Day 2 Valid 12Z Tue Aug 19 2025 - 12Z Wed Aug 20 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTH-CENTRAL PLAINS TO GREAT LAKES, SOUTHERN APPALACHIANS, AND SOUTHWESTERN U.S...

...Southern Plains to Great Lakes...

Mid and upper level progression will undergo a wave break pattern
with the eastern flank of the ridge being compressed with an
overall shift westward in the ridge axis leading to energy dropping
southeast out of the Great Lakes area. Widespread +1 to +2
deviation PWATs will exist in proximity of the Missouri Valley up
into the Great Lakes with a cold frontal progression moving
southeast out of the Northern Plains into the Central U.S. by
Tuesday afternoon. Coupled low and mid-level ascent provided by
migrating shortwaves and the aforementioned front will interact
with the above normal moisture environment in place allowing for
widespread convective development across a large chunk of the
Plains up through the Ohio Valley and Great Lakes creating a broad
threat for localized flash flooding. Greatest potential will likely
exist over the Mid-Mississippi Valley into the western Ohio Valley
given the strongest low-level convergence signature and mid-level
shortwave focus in tandem for Tuesday afternoon and evening. Areal
average QPF output still isn't as robust as one would look for to
entice an upgraded risk, however there are some early indications
from the end of the CAMs window where perhaps a targeted upgrade
could occur if the trends remain favorable for the outlined area.
Locally as much as 3" are indicated in that zone with some 2-3"
totals littered across the Central U.S in proxy to the advancing
cold front. First Guess Fields remain consistent on just a broad
MRGL risk area which was general continuity from previous forecast.
As a result, maintained that posture, but will monitor for the
upgrade potential in the succession of updates.

...Southern Appalachians...

Elevated moisture and narrow tongue of instability in the confines
of the Southern Appalachians will allow for a threat of focused
heavy rainfall across the western Carolinas down into GA. A quick
moving mid-level perturbation dropping south out of the Ohio Valley
will enhance the potential providing just enough forcing and weak
shear to warrant some heavier convective outputs capable of
dropping 2-3" in a short time that would generate some flash flood
prospects in the vicinity of the complex terrain. Previous forecast
was still on target with the latest model trends leading to
relative continuity in the MRGL in place.

...Southwest...

Little to no change in the expected pattern evolution across
portions of the Southwest U.S. with regards to convective
opportunity. Remnant moisture with PWAT anomalies around 1 standard
deviation above normal will be situated over eastern AZ/much of NM
on Tuesday. Considering the moist environment in place, hourly
amounts between 1-2" are plausible where cells stall, backbuild,
merge, or train. An isolated terrain driven flash flood risk is
possible in the diurnal convection, especially over the Sangre de
Cristos, Sacramento's, and eastern Mogollon Rim. Considering run to
run variance being limited over the past 24 hrs., there was no
reason to deviate much from the inherited forecast. The MRGL risk
was generally maintained with some minor adjustments on the
northern periphery to account for QPF enhancement in-of the Sangre de Cristos.

Kleebauer


Day 3 Valid 12Z Wed Aug 20 2025 - 12Z Thu Aug 21 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN EFFECT FROM
THE SOUTHERN PLAINS TO CENTRAL AND SOUTHERN APPALACHIANS, AND
SOUTHWEST U.S...

...Southern Plains to Appalachians...

Slow migrating cold front will become the focal point for
convective development over the course of Wednesday into early
Thursday leading to widely scattered thunderstorms capable of
localized flash flooding. Signal is really diffuse overall, but
environmental conditions are still relevant for pockets of heavy
rain that could cause some flash flood concerns in more urbanized
corridors of the Southern Plains to the southern half of the
Appalachian front. The best potential likely exists in the
mountains where complex terrain and convergent flow will aid in
upslope forcing capable of slow-moving cell motions and heavy
rainfall over smaller foci (mountain ridge tops). A low-end MRGL
exists over a broad area with potential for a more concrete area of
interest pending how the broad synoptic pattern evolves and any
focal points within the mesoscale (remnant outflows).

...Southwest...

Monsoonal moisture presence and general diurnal instability will
aid in traditional afternoon and evening convective output across
east and southeast AZ into west-central NM on Wednesday. Signals
for heavy precip are very isolated leading to the threat lying just
inside the MRGL risk threshold. There is a chance the areal
coverage shrinks or the threat goes away altogether, but model
output maintains the prospects at this juncture, so maintained
continuity from previous forecast.

...Northern Mid Atlantic...

As of this update, there is no risk area in place across Central PA
into New York State, however will be monitoring the pattern
progression of a shortwave ejecting out of Ontario by the end of D2
into D3 that could entice a targeted risk in these two specific
zones. Models are truly split on the threat, and with antecedent
conditions running very dry over the areas in question, it will
take guidance amping up the precip output to consider any upgrades.
This has some definition within the ML guidance and EC ENS, so
wanted to provide some insight on the threat despite a lack of a risk area.

Kleebauer
$$
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FOUS30 KWBC 190817
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
417 AM EDT Tue Aug 19 2025

Day 1 Valid 12Z Tue Aug 19 2025 - 12Z Wed Aug 20 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR A PORTION OF
THE SOUTHERN APPALACHIANS...

...Southern Appalachians...
Old frontal boundary strengthened by 'cold' air damming,
northeasterly flow has pooled enhanced low to mid-level moisture
through the eastern slopes of the Southern Appalachian mountains.
Another day of slow southward sag of the boundary, clearing skies
for ample insolation across the terrain and strong upslope should
trigger solid convective response through early afternoon. A narrow
mid-level ridge to the northwest will keep weak mid to upper level
steering in place to allow for slow cell motions with potential of
continued upslope convergence resulting in scattered clustering
and potential cell mergers. Hi-Res CAMs continue to paint the
eastern slopes of the NC and NE GA Appalachians with 2-4" totals
resulting in HREF neighborhood probability of 3" at 40-50% and
indications of 5"+ at 20%. Total moisture is not overly anomalous,
but is still above average, though persistent upslope flux in
complex terrain suggests a small Slight Risk of Excessive Rainfall
appears prudent at this time.

...Coastal Plains of Southern Maryland to Georgia...
Reinforcing cold front has stalled across the southern Mid-
Atlantic Monday that has pooled enhanced moisture near the mouth of
the Chesapeake Bay through the Coastal Plains of the Carolinas,
connecting back to an older cold front and pool across east-central
GA. Total Pwats of 2" are pooled along the boundary. As such, this
will tighten moisture/theta-E gradients and with ample early
morning insolation should make for an unstable convective
environment by afternoon. Additionally, slow approach and influence
of Hurricane Erin, will maintain/tighten moisture/instability
gradient and strengthen sea-breeze development. Given strong low
level convergence; weak,parallel to coast mid to upper level
steering; especially near intersection with front extending out
from SE VA, localized rates of 2-2.5"/hr are probable and with deep
layer steering generally parallel to the Coastal Carolinas, some
short- term repeating is possible before propagating inland
resulting in some localized totals of 2-4" with highest
probabilities further north in SE VA/NE NC.

...Great Lakes to eastern Central Plains...
Mid to upper level progression depicts ridge building across the
Northern Plains as broader shortwave feature rolls into a weakness
across the Great Lakes later today (Tuesday); with the amplifying
ridge, further elongation of a positive trough weakness expands
southward toward the Ozark Plateau and eastern Central Plains. The
associated surface low and cold front will progress through the
central Great Lakes into the Northeast toward end of day supporting
relatively stronger moisture flux along it and through the eastern Midwest/Northern Ohio Valley with slightly above average PWat
values of 1.5-1.75"; locally higher to provide ample moisture for
efficient rainfall and localized scattered to widely scattered
flash flood risk. Deeper layer moisture is slightly reduced further
southward along the sagging frontal zone into the Mid-MS River
Valley and Ozarks, but to counter-act the reduction in
coverage/rainfall efficiency; cell motions will be slower and more
chaotic in nature to allow for increased duration/random mergers
to occur than farther north across W NY/MI/OH and IND. Hi-Res CAM
signals remain on course for random/scattered incidents of 2-3"
totals consistent with a broad Marginal Risk area across the Great
Lakes/Ohio Valley into the Central Plains. This remains on track to
prior forecasts, with only small adjustment to connect risk areas
to the Marginal Risk across the Southern High Plains and western
Central Plains (see below).

...Southwest to Southern High Plains...
As noted in section above, broad 1.5 to 2 standard anomaly ridge
continues to dominate the central Rockies, spreading into the
northern High Plains. This shift allows for shortwave 'ridge-
rider' energy to further erode and retrograde along its southeast
quadrant. As such, another day of active thunderstorms within an
above average low-level moisture plume will unfold centered over
NM. Hi-Res CAMs and HREF show highest signal along the early
afternoon upslope/convergence along the Sangre de Cristo,
Sacramento, Mogollon and Black Ranges. Eventually spreading out
with scattered to widely scattered slow moving pulse cells across
the southern Central Plains and southern High Plains into the
evening hours. High rainfall production and slow/stationary cell
motions will result in scattered instances of 2"+ resulting in
widely scattered possible flash flooding consistent with a Marginal
Risk of Excessive Rainfall.

Gallina


Day 2 Valid 12Z Wed Aug 20 2025 - 12Z Thu Aug 21 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN EFFECT FROM
SOUTHERN NEW ENGLAND DOWN THE APPALACHIANS, THE MID-SOUTH AND TEXAS,
AS WELL AS EASTERN ARIZONA...

...Northeast...
Stationary front lingering over the northern Mid-Atlantic looks to
form a convergent focus to moisture streaming north ahead of
Hurricane Erin, particularly Wednesday night. This front and
enhanced moisture (The 00Z ECMWF retains PW around 2"), along with
the area from Long Island/NYC to southern New England in
a right entrance region of a Wly jet that extends over the Gulf of
Maine continue to point to a possible predecessor rain event (PRE).
For now the Marginal is expanded per 00Z guidance consensus
(connecting to the previous Marginal on the Appalachians) with a
note that there very well may be upgrades needed once the target is
more clear.

...Southern Plains through the Appalachians...
Slow migrating cold front is the continued focal point for
convective development Wednesday leading to widely scattered
thunderstorms capable of localized flash flooding. Environmental
conditions are conducive for pockets of heavy rain that would
cause some flash flood concerns in urban centers of the Southern
Plains through the Appalachians. Enhanced rainfall is expected in
the mountains where complex terrain and convergent flow will aid in
upslope forcing capable of slow- moving cell motions and heavy
rainfall. A broad low-end Marginal persists over a broad area with
potential for enhanced areas pending how the broad synoptic and
localized mesoscale (boundaries) pattern evolves.
The Marginal risk was expanded west through the Sacramento
Mountains where CAMs are once again focusing enhanced diurnal convection.

...Southwest...
Monsoonal moisture presence (1.5 sigma above normal) and general
diurnal instability will aid in traditional afternoon and evening
convective output across east and southeast AZ into west-central NM
on Wednesday. The Marginal Risk is retained.

...Eastern North Carolina...
Moisture plume from Erin with 2" PW converges on surface trough
over far eastern NC providing a corridor of enhanced rainfall.
Also, uncertainty in the track of Erin may bring the outer bands
close enough to warrant an excessive rainfall risk. This rainfall
looks to be on the order of a couple inches, but also comes during
an approaching new moon with swell that may locally worsen
drainage. A Marginal Risk is introduced for the Outer Banks.

Jackson


Day 3 Valid 12Z Thu Aug 21 2025 - 12Z Fri Aug 22 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE
SOUTHWEST, SOUTH-CENTRAL TEXAS THROUGH THE SOUTHEAST, AND THE
NORTHERN PLAINS INTO MINNESOTA...

...Southwest...
Lingering monsoonal moisture (PW one sigma above normal) and
diurnal instability will trigger afternoon and evening showers and
storms across most of central and eastern Arizona, southern Utah,
and northwestern New Mexico. Heavy precipitation should be
localized, but could cause flash flooding concerns for sensitive
areas (steep terrain, burn scars, urban areas). The Marginal Risk
is retained with some overall expansion for the above mentioned
areas for this isolated flash flood threat.

...South-Central Texas through the Southeast and Southern
Appalachians...
A slow-moving frontal boundary will sag farther into the southern
states on Thursday and continue to serve as a focus for scattered
showers and storms from south-central TX to western NC. Diurnal heating/instability and a broad swath of anomalous moisture will
support locally heavy rain that could lead to isolated instances of
flash flooding, especially in urban, poor drainage, and/or low-
lying areas. Overall, convective organization looks like it will be
lacking, but heavy rain may be more concentrated over the southern
Appalachians with upslope enhancement. Furthermore, the greatest
moisture anomaly is over Louisiana, so that area may be a target
for an upgrade should it become apparent in CAM solutions. A broad
Marginal Risk is in place to cover this activity from the southern
Plains to the southern Appalachians with some expansion east to the
central Carolinas.

...Northern Plains and Upper Midwest...
An energetic upper-level shortwave is forecast to move east across
the northern Plains and Upper Midwest Thursday afternoon and night.
This will be accompanied by a strong surface cold front that moves
through moisture and instability to support at least locally heavy
rain rates with showers and storms. The front should be fairly
progressive, limiting heavy rain potential, but convective mode
will play a role in determining heavy rain/flash flood threats in
this area. For now, there Marginal Risk over the eastern Dakotas
and much of MN is expanded south to include more of SD per the 00Z
RRFS and Canadian Regional output.

...Eastern North Carolina...
Moisture convergence from Erin and possibly outer bands continue
over the Outer Banks into Thursday warranting a continuation of the
Marginal Risk from Wednesday.

Dolan/Jackson
$$
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FOUS30 KWBC 200814
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
414 AM EDT Wed Aug 20 2025

Day 1 Valid 12Z Wed Aug 20 2025 - 12Z Thu Aug 21 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN EFFECT FROM
SOUTHERN NEW ENGLAND DOWN THE APPALACHIANS, THE MID-SOUTH AND TEXAS,
AS WELL AS EASTERN ARIZONA...

...Northeast...

Combination of a transient shortwave out of Canada and a flux of
moisture from the Atlantic will generate a period of heavy rainfall
potential in-of the interior Northeast across Southern New England.
Reasonable consensus in the handling of the shortwave progression
among models lends credence to the MRGL risk forecast over NY state
down into northern PA, but still some questions exist on the threat
of heavier precipitation into parts of Southern New England. The
greatest probs from NBM and HREF indicate the area from the
Berkshires over into the Hudson Valley as the primary target for
heavy rainfall that could exhibit threats for flash flooding,
mainly in more urbanized settings given very dry antecedent
conditions. Over into Southern New England to the east of the
Berkshires, there's discrepancy on the handling of the moisture
advection pattern and potential convergence along the northern edge
of Hurricane Erin in the Western Atlantic and the surface ridge in
place over maritime Canada. HREF means tend to limit the scope of
the threat for heavy rainfall to more isolated east of the Hudson
and Berkshire areas with some guidance indicating a stripe of heavy
rainfall bisecting portions of MA/CT/RI before fizzling out the
back end of the forecast. There's still some deterministic hanging
on the idea of more prolific rainfall across LI up into Southeast
MA and neighboring CT/RI, but that seems to have less agreement
among even the individual ensemble members as the timing of the IVT
pulse and connection with the transient shortwave might just miss
the potential for a more textbook Predecessor Rainfall Event (PRE).

HREF EAS probs for >1" remain elevated (50-70%) across the Hudson
and Catskill areas of NY state over into the western slopes of the
Berkshires. EAS probs for >2" drop off significantly with less
consensus on the higher end threat in the same zone with even less
signal further east where a PRE would be most prominent if one
evolved. EC AIFS ENS has been steady with the projection of the PRE
just barely missing with the 850-700mb moisture flux converging off
the LI/SNE coast and moving out to sea with maybe places like
Nantucket and eastern Suffolk the beneficiaries of the heavier
precip potential from a PRE organization. This is still the less
likely among the ensemble members and deterministic suite, so
generally stayed away from any higher risk implementation unless we
see greater consensus.

The MRGL risk from the previous forecast was unchanged in this
forecast with a threat of convectively driven rainfall most aligned
from I-80 and points south with more dynamical heavy rain support
for areas north where the shortwave will traverse. Pockets of
convection exhibiting 1-2"/hr will be plausible in-of the Mid
Atlantic urban corridor with the best threat likely between I-70
and I-80 across MD/PA/NJ to the east of the Blue Ridge. Some
guidance have been indicating a localized maxima over Southern NJ
near the Philadelphia metro, likely attributed to some convergence
from the advection pattern to the south and mid-level perturbation
migrating across Southern PA. Something to monitor over the course
of CAMs output.

...Southern Plains through the Appalachians...

Slow migration of a cold front through the central and eastern
CONUS will continue into Wednesday as the frontal progression will
lead to yet another focus of convection firing near and along the
front as it moves into a more favorable environment of elevated
moisture and instability. There are two areas of interest for today
with regards to more regional maxima in QPF; one over east TX and
the second over the Central Appalachians in WV/southwest VA. Both
are amplified in the threat due to the approach of mid-level energy
that will enhance convective development during peak diurnal
destabilization. WV into VA will have the assistance of terrain to
help with the evolving convergence pattern as the front migrates
into the Appalachian front later today. Some of the CAMs output has
been relatively robust for the region in question with HREF
neighborhood probs for >2" running between 60-80% from the Smoky
Mountains, northeast through the WV Highlands and Southern Laurels
in PA. Environment favors this area considering the pronounced
theta_E tongue situated over the above locations, a signature that
exemplifies the best proxy for greatest instability/thermodynamic
support. Mean flow remains on the lighter side as well with the
expectation for storms to move slowly and drift more east to
southeast with the steering pattern. This sets up well for locally
heavy rainfall in those complex terrain areas of the Appalachians
leading to more of a risk of flash flooding in adjacent valley
towns. Considering some of the drier antecedent conditions and more
localized flash flood prospects, the MRGL risk was maintained from
the previous forecast, but if guidance trends upward in the
potential, would not be shocked to see a targeted upgrade in the
next update.

The threat over TX is more simplified with an abundance of surface
based instability as SBCAPE is forecast to be between 2000-3500
J/kg across east TX with the frontal approach. PWATs pooling to
between 2-2.25" based on areal average forecast from the HREF along
with the instability maxima leads to a threat of 2-3"/hr rates with
higher instantaneous rates that could easily subject areas from LA
over into east TX to see localized flash flood concerns. There's
not a particularly organized zone of convection being forecast with
more of a scattered signature among the CAMs, so the threat is
truly localized and falls well within the MRGL risk threshold.
Thus, little changes were necessary from the previous forecast.

...Southwest...

Monsoonal moisture and strong diurnal destabilization will yield
another day of widely scattered heavy rain prospects across the
higher terrain of eastern AZ into far western NM. The main areas of
concern will continue to be the Huachucas in Cochise county AZ and
across the eastern Mogollon Rim to the north. There's no real
organized signature to point out that could yield a higher risk
area, so the MRGL risk was generally maintained with little to no
adjustment.

...Eastern North Carolina...

Outer periphery of Hurricane Erin will lead to an uptick in
regional moisture as signaled by a consistent PWAT increase to
above 2" across Cape Hatteras and neighboring areas within the
Pamlico sound. The threat for >2" remains low with the primary
concerns likely the combination of locally heavy rain coupling with
coastal flooding to exacerbate areal flood concerns across the
Outer Banks. Tropical Storm Warnings remain in place with locally
heavy rainfall wording in the forecast from outer bands, so to
remain consistent with messaging, elected to maintain continuity
from previous forecast as the threat has not wavered the past 24 hrs.

Kleebauer


Day 2 Valid 12Z Thu Aug 21 2025 - 12Z Fri Aug 22 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHEAST, SOUTH-CENTRAL TEXAS, SOUTHERN APPALACHIANS, EASTERN
NORTH CAROLINA, UPPER MIDWEST, AND SOUTHWEST U.S...

...Southwest...

Elevated monsoonal moisture lingering under the western ridge will
lead to yet another afternoon of scattered convective development
across much of the desert Southwest and accompanying terrain.
PWATs running slightly above normal across the region will provide
just enough deep layer moisture to couple with relevant diurnal
buoyancy to account for periods of heavy rainfall in some of the
stronger convective cores that materialize Thursday afternoon into
the evening. Totals generally will fall <1" over the Southwest when
looking at areal averages, however some 1-2" totals are certainly
plausible in the setup with the best threat for impacts likely in
those slot canyon areas, drainage across complex terrain into
adjacent valleys, and remnant burn scar locations. The previous
MRGL forecast was generally maintained with only minor adjustments
to the edges of the risk.

...Texas through the Southeast and Southern Appalachians...

Our slowly progressing front will continue to wander further south
with yet another day of convective firing near and along the front
as it migrates through south-central TX and towards the Gulf
coast. The front will arc back into the Southern Appalachians where
scattered thunderstorm activity is likely to occur for at least one
more day in the terrain with the northern extent extending up into
Southern WV and Southwest VA. The signal is still scattered in
terms of convective coverage and flash flood prospects leaning
towards isolated when assessing the HREF probs for hourly rates
and FFG exceedance probs in the 12-00z window Thu/Fri. Convection
will likely dissipate slowly after sunset with the loss of diurnal
heating and surface decoupling putting a cap on the threat. Totals
between 3-5" are most common among some of the stronger cores in
guidance, a target that characteristically covers a MRGL risk with
some targeted SLGT risk opportunities if the signal becomes more
favorable within a favored area for flash flooding (IE: urbanized
zones and terrain). For now, the MRGL risk from previous forecast
was generally maintained with minor adjustments based on 00z QPF footprint.

...Northern Plains and Upper Midwest...

An energetic upper-level shortwave is forecast to move east across
the northern Plains and Upper Midwest Thursday afternoon through
the overnight. A strong cold front trailing a strengthening surface
low over southern Canada will aid in surface based forcing to
couple with the improving mid and upper dynamics as the trough
migrates along the Canadian border. Sufficient buoyancy and
moisture anomalies of 1-2 deviations above normal will exist along
and ahead of the front coinciding with a strong, yet progressive
line of thunderstorms that will be capable of isolated flash flood
prospects thanks to hourly rates between 1-2"/hr expected. Guidance
remains steadfast in its interpretation of the setup lending
confidence in maintaining continuity from previous forecast with
only small adjustments on the western flank of the risk area to
account for timing adjustments.

Kleebauer


Day 3 Valid 12Z Fri Aug 22 2025 - 12Z Sat Aug 23 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHWEST, SOUTHEAST, AND CENTRAL ROCKIES ...

...Southwest to Central Rockies...

Western ridge will shift to the west by the end of the week with
the monsoonal moisture pattern also migrating westward to include
more of the Great Basin and areas around the Colorado river basin.
PWAT anomalies ~ +1 deviation and strong surface destabilization
will yield a fairly widespread convective regime across the
Southwestern part of the CONUS with heavy rain signatures littered
among the activity. Rates up to 1-1.5"/hr in the strongest cores
will likely promote flash flood concerns in those more prone dry
washes, slot canyons, and burn scars residing over the region. The
threat extends into the Central Rockies as shortwaves round the
eastern flank of the ridge and aid in convective initiation over
the terrain of Central CO. Signal currently runs within the MRGL
threshold, but will assess for prospects of targeted upgrades if
any specific area stands out as we get closer to the event with CAMs input.

...Southeast...

The slow-moving front that will plague the South through the week
will finally hit a road block once it reaches the Gulf coast
becoming a focal quasi-stationary front by Friday morning.
Hurricane Erin will be exiting off into the northwest Atlantic by
this point, but the prominent in-flow trailing the storm will
continue across the Western Atlantic leading to pooling moisture
situated along the confines of the boundary. PWATs will surge with
areal average 2.25-2.5" encompassing a majority of the Gulf coast
from LA over towards the Southeast coastal plain between
Wilmington, NC down into northern FL. The combination of elevated
deep layer moisture, instability, and enhanced surface convergence
along the front will yield some fairly prolific rainfall makers in
any convective scheme during the period. The best signature for
heavy rain is more likely to occur over the SC/GA coast where
there's a stronger sfc-850mb convergence signature near the coast
leading to an area of ~2" of precip currently forecast in the area.
This is even prior to hi-res model forecasts, a testament to a
growing signature for heavy rain prospects that could very well
necessitate an upgrade in future forecasts, especially as we add
more CAMs input. For now, a broad MRGL exists across a good portion
of the Southeastern U.S.

Kleebauer
$$
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FOUS30 KWBC 220841
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
441 AM EDT Fri Aug 22 2025

Day 1
Valid 12Z Fri Aug 22 2025 - 12Z Sat Aug 23 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF
SOUTHEAST GEORGIA AND SOUTHERN SOUTH CAROLINA...

...Upper Midwest...
On-going shower and thunderstorms with locally heavy rainfall rates
mainly over eastern South Dakota preceding the start of the Day 1
period at 22/12Z should persist beyond 12Z. The expectation is that
the risk of excessive rainfall should diminish within a couple of
hours. Until then...locally heavy rainfall rates in excess of 1.5
inches per hour could result in flash flooding. Additional details
in WPC Mesoscale Precipitation Discussion 0972.

...Southeast...

A slow-moving front which becomes a quasi-stationary front upon
reaching the Gulf later today will be a focus for heavy to
potentially excessive rainfall. Precipitable water values with
areal average 2.25-2.5" encompassing a majority of the Gulf coast
from LA over towards the Southeast coastal plain. This...combined
with elevated deep layer moisture, instability, and enhanced
surface convergence along the front will yield some fairly prolific
rainfall makers in any convective scheme during the period. Latest
HREF/RRFS runs still key in the Georgia/South Carolina area
(especially coastal areas) due to stronger sfc-850mb convergence.
Areal average rainfall of ~2-3" of rainfall remained in the latest deterministic QPF.

The most robust signal was within the probabilities for FFG
exceedance just based off the 22/12Z to 23/00Z window still
indicated a greater than >60% chance of both 3hr and 6hr FFG
exceedance probabilities...generally from Charleston, SC down
through the SC Low Country into far southeast GA. Rainfall rates
will be pretty stout considering the environmental factors...with
classic tropical convective scheme that is capable of producing
2-3"/hr rates more regularly in the strongest cell cores, even
seeing 4-5"/hr instantaneous rates.

...Texas and Louisiana Gulf Coast...

Pooling moisture along a shallow quasi-stationary front along the
Gulf coast will amplify environmental conditions to favor isolated
to scattered convective development capable of localized flash
flooding thanks to deep layer moisture between 2-2.25" precipitable
water values and slower mean cell motions. The signal is not as
prolific as areas downstream, but the threat is still being
forecast based off the latest CAMs with some localized totals of
2-4" being forecast along and south of I-10, enough to maintain
general MRGL risk continuity from previous forecast.

...Southwest to Central Rockies...

Little change was necessary given run to run continuity on the
next widespread convective pattern centered over the Southwestern
CONUS to Central Rockies. Western ridge will shift towards the
Great Basin/Four Corners by the end of the week with the monsoonal
moisture pattern also migrating westward to include more of the
Great Basin and interior Colorado river basin. The amount of dry
air in the sub-cloud region of area sounding allowed for a bit of
area to be trimmed off the western and northern portion of the
Marginal risk area....but maintained it in the area of terrain.
Precipitable water anomalies on the order of +1 deviation and
strong surface destabilization will yield a fairly widespread
convective regime across the Southwestern part of the CONUS with
heavy rain signatures littered among the activity. Rates up to
1-1.5"/hr in the strongest cores will likely promote flash flood
concerns in those more prone dry washes, slot canyons, and burn
scars residing over the region. The threat extends into the Central
Rockies as shortwaves round the eastern flank of the ridge and aid
in convective initiation over the terrain of Central Colorado.

Overall...the current Excessive Rainfall Outlook changed little
provide the previous one.

Bann


Day 2
Valid 12Z Sat Aug 23 2025 - 12Z Sun Aug 24 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE CENTRAL AND SOUTHERN APPALACHIANS, SOUTHEAST AND SOUTHWEST U.S...

...Southeast into the Appalachians...

Elevated precipitable water values will linger across the
Southeastern CONUS through the first half of the weekend as a
stalled front leads to sustained pooling due to prolonged surface
moisture flux convergence. A modest surge in moisture along the
Appalachian front from Georgia up through West Virginia on
Saturday afternoon and beyond allowing for more scattered
convective signatures to materialize with the aid of diurnal
destabilization. Totals across the Southeast and Appalachians are
not as robust compared to previous periods to warrant anything
greater than a MRGL, however antecedent soil conditions over
portions of the Carolina's and Georgia may necessitate a targeted
upgrade. Given the trend for at least some modest convective
coverage through the morning and afternoon time frames on Saturday,
so there's a non-zero possibility of warranting a greater risk.
For now, kept the previous forecast over the Southeast with some
tweaks on the northern edge of the MRGL in the Appalachian front.

...West...

Little change in the large-scale pattern resulted in few changes
needed to the previous Day 3 outlook as it propagates into the Day
2 period. Numerous convection across southern and eastern
California and across the interior west with the eastern extent
likely back over the Central Rockies. Ridging over the western
CONUS will remain stationary with a recycled vorticity pattern
rotating under the guide of the ridge with elevated moisture pretty
much encompassing the Southwestern U.S and interior portions of
the west like NV/UT/CO. Heaviest QPF footprint is currently
situated over the Sangre de Cristos and San Juan Mtns given
embedded shortwave energy and orographics providing areas of focused
ascent. The more prone slot canyon, burn scar remnants, and dry
washes will once again be the target of interest for flash flood prospects..

Bann


Day 3
Valid 12Z Sun Aug 24 2025 - 12Z Mon Aug 25 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER THE
SOUTHWEST U.S. TO THE CENTRAL PLAINS AND ACROSS PARTS OF THE
APPALACHIANS AND MID-ATLATNIC...

...West...

Little change in the large-scale pattern spells another day of
scattered to numerous late day and evening showers and
thunderstorms for the areas generally west of the Rockies. A shift
in the mid-level flow may allow for increasing amounts of moisture
to start a slow northward expansion across parts of the
Intermountain region...resulting in an expansion to the Marginal
Risk area there. Otherwise...the driving forces will continue to be
weak shortwave energy embedded within fast flow...locally encountering/interacting with orographics during the time of
maximum heating/instability. Once again...slot canyons, burn scar remnants,
and dry washes will once again be the target of interest for flash
flood prospects..

Father east...the risk of excessive rainfall starts to spread out
away from the central Rockies Front Range and out over the adjacent
plains where any shortwave energy encounters lowering mid-level
heights. Flow aloft is forecast to be northwesterly at this point
but models do show a period of low level upslope flow. Spaghetti
plots do show some potential for 2 to 3 inch rainfall amounts
extending as far east as western Kansas by the end of the period.
Given the precipitable water values forecast...the most active
convection could drop 1 to 2 inch rainfall amounts in an hour.

...Appalachians to Mid-Atlantic and Pennsylvania/New York...
A deepening area of low pressure north of the border will force a
cold front to sweep eastward from the Great Lakes into the eastern
third of the country on Sunday...driven in part by a 75 to 100 kt
upper level jet providing support via divergence aloft. With the
renewed push of colder air...the low level boundary will act to
focus shower and thunderstorm activity capable of locally heavy
rainfall rates that could challenge flash flood guidance-
especially in areas where flash flood guidance has been suppressed recently.

Bann
$$
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FOUS30 KWBC 230838
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
438 AM EDT Sat Aug 23 2025

Day 1
Valid 12Z Sat Aug 23 2025 - 12Z Sun Aug 24 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHEAST AND FOR PORTIONS OF THE CENTRAL/SOUTHERN ROCKIES...

...Southeast into the Appalachians...

Convection that occurred on Friday has increased the amount of soil
saturation and consequently the sensitivity for flooding from
additional rainfall. With similar environmental conditions
today... 1500 to 2500 J per kg of CAPE, lingering mid- and upper-
level vorticity aloft with a weak circulation center hugging the
Georgia/South Carolina coastline and elevated precipitable water
values...there will an elevated threat for scattered areas of flash
flooding across the region particularly for Georgia and the
coastline. Areal averages of 1 to 2 inches will be common with
very isolated maxes upwards of 4 to 6 inches remain possible near the coast.

...West...

Little change in the large-scale pattern resulted in the Excessive
Rainfall Outlook being very similar to the one on Friday. Scattered
to numerous showers and thunderstorms across southern and eastern
California and across the interior west with the eastern extent
likely back over the Central Rockies. Heaviest QPF footprint is
currently situated over the Sangre de Cristos and San Juan
mountains southward into northern New Mexico given embedded
shortwave energy and orographics providing areas of focused ascent.
The more prone slot canyon, burn scar remnants, and dry washes
will once again be the target of interest for flash flood
prospects with model guidance continuing to show localized maximum
rainfall rates on the order of 1 to 1.5 inches during the time of
maximum heating that persists into the evening.

Bann


Day 2
Valid 12Z Sun Aug 24 2025 - 12Z Mon Aug 25 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER THE SOUTHWEST
AND FOR PORTIONS OF THE CENTRAL ROCKIES TO THE CENTRAL PLAINS...

...West...

Maintained the Slight Risk area in parts of Utah and northern
Arizona where models still depict convection occurring over/near
vulnerable slot canyons, burn scars and normally dry washes during
from later today into the evening...much like the placement and
timing of storms that occurred on Friday. The driving forces will
continue to be weak shortwave energy embedded within the
anticyclonic flow across the Intermountain region.

Father east...the risk of excessive rainfall starts to spread out
away from the central Rockies Front Range and out over the adjacent
plains. Deep layer shear is going to be enhanced as the flow aloft
is forecast to be northwesterly at this point while low level flow
from the southeast draws air with higher dewpoints/precipitable
water values upslope. Spaghetti plots along with the RRFS continue
to show potential for 2 to 3 inch rainfall amounts extending as
far east as western Kansas by the end of the period. Given the
precipitable water values forecast...the most active convection
could drop 1 to 2 inch rainfall amounts in an hour. The previously
issued Slight was largely unchanged.

...Appalachians to Mid-Atlantic and Pennsylvania/New York...

A deepening area of low pressure north of the border will force a
cold front to sweep eastward from the Great Lakes into the eastern
third of the country on Sunday. The airmass ahead of the front
across the central and southern Appalachian chain is forecast to
have 500 to 1000 J per kg of MLCAPE and precipitable water values
generally in the 1.5 to 1.75 inch range at the start of the day
which drops during the day. The area over portions of Pennsylvania
and New York continue to have a longer window of opportunity for
locally heavy rainfall. As a result...maintained the northern end
of the Marginal risk area near a region of lower flash flood
guidance due to the potential for heavier rainfall rates and
amounts overlapping.

...Coastal North Carolina...
A weak surface feature hugging the coastline will focus and
support locally heavy rainfall near the coast of North Carolina on
Sunday and Sunday night. Present indications are that the activity
should remain off-shore. However...even a subtle slowing of its
forward speed or shift in track could bring moderate to heavy
rainfall to the immediate coastline of North Carolina late Sunday.

...Southern Georgia and northern Florida...
On-shore flow of moist air interacting with the southern end of the
front associated with the low pressure/amplifying upper trough to
the north should combine for convection capable of producing heavy
rainfall Monday and Monday evening across portions of southern
Georgia into the northern Florida peninsula.

Bann


Day 3
Valid 12Z Mon Aug 25 2025 - 12Z Tue Aug 26 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL ROCKIES FRONT RANGE TO THE SOUTHERN PLAINS ON MONDAY...

Broad, cyclonic flow aloft will be in place across the Plains on
Monday while low level flow should continue to be drawn northward
at low levels of the Southern Plains...with a boundary extending
front northern Texas into northeast New Mexico and southern
Colorado helping to focus late day storms. The airmass south of the
front is expected to have precipitable water values approaching 2
inches across the region and values potentially in the 2 to 2.25
inch range near the Red River. Stability does not appear impressive
at this point...but the atmosphere should support locally heavy
rainfall should convection develop anywhere between
Oklahoma/northern Texas westward into the plains of eastern
Colorado and northeast New Mexico.

The Slight Risk area was embedded within a broader Marginal Risk
area extending across much of the central and southern portion of
the Great Basin and eastward to the central and southern Rockies
Front Range. Once again...weak shortwave energy embedded within a
broad upper leads to yet another round of late day showers and
thunderstorms. Slot canyons...normally dry washes and burn scars
remain most at risk for flooding.

Bann
$$
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FOUS30 KWBC 240835 AAA
QPFERD

Excessive Rainfall Discussion...UPDATED
NWS Weather Prediction Center College Park MD
435 AM EDT Sun Aug 24 2025

Day 1
Valid 12Z Sun Aug 24 2025 - 12Z Mon Aug 25 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER THE SIERRA,
SOUTHERN UTAH, AND THE WESTERN HIGH PLAINS...

...Intermountain West to the Central Plains...

With the finer scale models maintaining and even bolstering their
signal for enhanced rainfall amounts for the Sierra Nevada range eastward/northeastward...maintained the Slight Risk area with few modifications. In places...this rainfall will be in addition to
some noteworthy rainfall amounts that fell on Saturday. With such
anomalous moisture being pulled northwestward around the upper
high/ridge axis...the expectation is that sufficiently high
rainfall rates are possible that excessive rainfall is a concern
across more the the intermountain region today compared with Saturday.

Father east, the risk of excessive rainfall starts to spread out
away from the Front Range of the central Rockies, and out over the
adjacent Plains in a region of low level southerly flow drawing
moisture northward while a broad area of surface high pressure at
the surface and fast northwest flow aloft pushes a cold front south
into parts of the central plains. This should set the stage for an
MCS later tonight across parts of Colorado that spreads eastward
and southward. The latest runs of the RRFS has been favoring
heavier rain in southwest Kansas and portions of the Oklahoma and
Texas panhandles...while the HREF has thrown in more with the
coarser/global models in heavy to potentially excessive rainfall
being confined to western Kansas. With the instability fields in
the NAM and RRFS depicting 1000 to 2000 J per kg in better upslope
flow closer to the Colorado state line...expanded the Slight Risk
area southward and westward a bit. The presence/persistence of any
low cloud cover that forms in the upslope flow will limit the
surface heating and shift the focus for storms capable of producing
heavy rainfall.

...Northern Mid-Atlantic and Pennsylvania/New York...

A strong upper trough making its way eastward from the Ohio Valley
and eastern Great Lakes should make it into Pennsylvania and New
York state before slowing. The airmass its moving into will have
500 to 1000 J/kg of MLCAPE and precipitable water values generally
in the 1.5 to 1.75 inch. With only modest low/mid level lapse
rates...a few of any storms that form could produce locally heavy
rainfall that results in localized flooding this afternoon or early
evening before convection wanes with the loss of daytime heating.

...Coastal Carolinas...

A weak surface feature in the vicinity of the coastline will focus
and support locally heavy rainfall near the coastal portions of
the Carolinas into tonight. Present indications are that the
activity should remain off-shore. However...on-shore flow and the
proximity of showers associated with the feature will keep the risk
of some brief heavy rainfall along the immediate coast today. Any
risk of excessive rainfall should taper off from south to north as
the system continues to move northeast.

...Southern Georgia and northern Florida...

On-shore flow of moist air interacting with the southern end of the
front associated with the low pressure/amplifying upper trough to
the north should combine to focus/support convection capable of
producing heavy rainfall Monday and Monday evening across portions
of southern Georgia into the northern Florida peninsula.

Bann


Day 2
Valid 12Z Mon Aug 25 2025 - 12Z Tue Aug 26 2025

...THERE ARE SLIGHT RISK OF EXCESSIVE RAINFALL AREAS OVER
PORTIONS OF THE CENTRAL ROCKIES FRONT RANGE AND THE SOUTHERN
PLAINS ON MONDAY...

Broad cyclonic flow aloft will be in place across the Plains on
Monday while south to southeasterly low level flow continues to be
drawn northward at low levels across the Southern Plains, with a
boundary extending from northern Texas into northeast New Mexico
and southern Colorado helping to focus another round of late day
storms once an MCS weakens and dissipates in the morning. The
airmass south of the front is expected to have PWs approaching 2
inches across the region and values potentially in the 2 to 2.25
inch range near the Red River. The overnight numerical guidance
still supports the idea of two distinct regions of rainfall and saw
little reason to make more than minor adjustments to the two Slight
Risk areas from the previous outlook. Instability does not appear
impressive at this point, but the atmosphere should support locally
heavy rainfall should convection develop anywhere between
Oklahoma/northern Texas westward into the plains of eastern
Colorado and northeast New Mexico.

The Slight Risk areas were embedded within a broader Marginal Risk
area extending across much of the central and southern portion of
the Great Basin and eastward to the central and southern Rockies
Front Range. Once again...weak shortwave energy embedded within a
broad upper leads to yet another round of late day showers and
thunderstorms. Slot canyons...normally dry washes and burn scars
remain most at risk for flooding.

Bann


Day 3
Valid 12Z Tue Aug 26 2025 - 12Z Wed Aug 27 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL AND SOUTHERN ROCKIES AS WELL AS ADJACENT PLAINS...

With a sprawling upper ridge in place...the potential exists for
excessive rainfall will exist as anomalously deep moisture
provides an environment supportive of brief but locally intense
rainfall rates from any daytime or evening storms that form. The
numerical guidance showed a more coherent signal for organized
heavy rainfall from southern Colorado into northern New Mexico
where low level flow is transporting moisture upslope and
instability peaks at around 1000 J per kg in the late day with shortwave
energy moving north-/northeastward across western New Mexico.

Bann
$$
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FOUS30 KWBC 250811
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
411 AM EDT Mon Aug 25 2025

Day 1 Valid 12Z Mon Aug 25 2025 - 12Z Tue Aug 26 2025

...THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL FOR SOUTHERN
ARIZONA AND OVER PORTIONS OF THE CENTRAL ROCKIES FRONT RANGE AND
THE SOUTHERN PLAINS...

Weather Pattern Summary...

A large portion of the southwestern U.S. remains mired in a
classic monsoonal moisture flow regime with broad ridging over the
Four Corners region on south into Mexico. An expansive area of
highly anomalous moisture content will remain firmly entrenched
over the West through mid-week with some of this moisture spilling
east into the Plains as frontal boundaries and a NW-SE oriented jet
stream direct some of this monsoonal moisture eastward. The ECMWF
ENS shows PWATs above the 90th climatological percentile from the
Pacific Northwest Coast to as far east as eastern Oklahoma. This
abundance of moisture is why there is an expansive Marginal Risk
area that stretches from southern Oregon and California's Sierra
Nevada to as far east as the Lower Mississippi Valley. Look for
storms today and through Monday evening to be capable of producing
torrential downpours throughout the Marginal Risk area in the West
that could result in flash flooding. For additional information on
the Slight Risks, please see below:

...Southern Arizona...

An influx of rich monsoonal moisture (PWATs 1.6-2.0") will engulf
much of southern AZ and the Lower Colorado River Valley Monday
afternoon and evening while MLCAPE ranges between 500-1,000 J/kg.
Storm motions will generally be <10 knots and vertical wind shear
is weak, but these storms will be loaded with heavy rainfall that
generate exceptional rainfall rates in a desert climate.
Thunderstorms will be capable of producing 2"/hr rainfall rates and
in some significant cases, as much as 1.5" in 30 minutes. Storms
will initially develop as a result of daytime heating, but additional
storms will form into Monday evening due to colliding outflows
producing storms that tap into lingering elevated instability.
Areas most at risk for flash flooding are in dry washes, arroyos,
and poor drainage areas.

...Central Rockies Front Range...

Low-level moisture advection into southeast CO and northeast NM
will coincide with a nearby frontal boundary to trigger additional
strong thunderstorms Monday afternoon and evening. PWATs remain
above the 97.5 climatological percentile within the Slight Risk
area and soils are becoming increasingly more saturated following
an active weekend. With PWATS >1.2" and MLCAPE >500 J/kg, hourly
rainfall rates could range between 1.5-2.0" at their heaviest
intensity. Given these factors, flash flooding is likely in areas
of complex terrain and near burn scars.

...Southern Plains...

Unlike the Southwest and the Rockies, there are more synoptic-
scale and mesoscale factors at play that will develop numerous
areas of thunderstorms capable of producing flash flooding. The
region resides beneath the diffluent right-entrance region of a
250mb jet streak that is located over the east-central U.S.. A
strong 850mb front will reside over the Slight Risk region with
modest 850mb warm-air advection being observed over the Southern
Plains. Not only is the moisture source initially from monsoonal
flow, but there is also some modest moisture advection at low-
levels that originates out of the northern Gulf. The result is a
surge in PWATs that approaches 2.0" in central OK and central AR
that will also have anywhere from 500-1,000 J/kg of MUCAPE to work
with through Monday night. Storms will flare up initially this
morning, then following a brief lull in thunderstorm activity
through early evening, a brief restrengthening of the LLJ will
trigger new storms Monday night and into Tuesday morning. Latest
HREF guidance shows low-to-moderate chances (20-45%) for rainfall

3" in eastern OK. The Slight Risk was adjusted to match more of

the QPF trends and the aforementioned HREF probabilistic guidance.

...Western Florida Peninsula...

A Marginal Risk was introduced over the more populated section of
western Florida given a rather noticeable 20-35% odds depicted by
the 00Z for 24-hour rainfall totals >5". The Tampa-St. Petersburg
metro area will have >2.2" PWATs and >1,000 J/kg of MLCAPE
available for storms to tap into, while at the same time, mean-
layer winds in the sfc-500mb layer are almost uniformly out of the
WSW. The concern is for training and back-building thunderstorms,
which is denoted by ECMWF area-averaged soundings around Tampa Bay
that feature Upshear Corfidi vectors that are <10 knots. Given
these factors, as well as these storms producing >3"/hr rainfall
rates over a more urbanized environment, a Marginal Risk was
introduced this forecast cycle.

Mullinax


Day 2 Valid 12Z Tue Aug 26 2025 - 12Z Wed Aug 27 2025

...THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL OVER PORTIONS OF
SOUTHERN ARIZONA AND THE CENTRAL ROCKIES...

...The West...

The sprawling upper ridge over the Southwest continues to funnel
monsoonal moisture northward through the Intermountain West. ECMWF
guidance shows PWATs in excess of 1" advancing as far north as the
Blue Mountains and Columbia River Valley of WA/OR. Some PWATs are
also expected to top 1.25" in portions of the Great Basin and Snake
River Valley. Helping to add some upper-level support aloft will be
the presence of a meandering 700mb low positioned over the Pacific
Northwest and a healthy diffluent pattern at 250mb thanks to a
longwave trough situated along the West Coast. With such high
moisture content, not much in the way of surface based heating will
be needed to spark widespread thunderstorms Tuesday afternoon and
through Tuesday evening. Combined with MUCAPE between 500-1,000
J/kg, thunderstorms will be capable of generating up to 1.5"/hr
rainfall rates, which will pose a flash flood threat in areas of
complex terrain and in nearby creeks and streams.

...Southern Arizona...

Fresh off a busy day of thunderstorms on Monday, there is the
possibility that the atmosphere is overworked to where converage of thunderstorms is not as expansive as Monday. However, southeast AZ
should have a greater concentration of instability (500-1,000 J/kg
of MUCAPE) and PWATs will remain as high as 1.5" in some cases.
This continues to support rainfall rates up to 2"/hr in the more
intense storms. While storms will remain more pulse-like in nature,
these potent storms will still pose a flash flood threat,
especially in dry washes and in spots that drain poorly.

...Central & Southern Rockies...

Guidance across the board shows a higher concentration of
atmospheric moisture over the region on Tuesday compared to Monday,
and that is notable considering PWATs were already above the 97.5 climatological percentile on Monday. PWATs in the tallest peaks
will generally hover near 1" at their highest values, but along and
just east of the Front Range, PWATs are likely to range between
1.3-1.5". These values are surpassing the 99th climatological
percentile while also having 250-500 J/kg of MLCAPE present. With
soils steadily growing more and more saturated and the favorable
atmospheric parameters in place, more instances of flash flooding
are expected with complex terrain and burn scars more at-risk.

Mullinax


Day 3 Valid 12Z Wed Aug 27 2025 - 12Z Thu Aug 28 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL PLAINS...

...Central Plains...

A sheared 500mb vort max exiting the Central Rockies will help to
spawn a surface low over the southern High Plains on Wednesday.
Working in tandem with the dome of high pressure to the east, this
will tighten the pressure gradient and prompt a strengthening LLJ
to form over the Southern Plains late Wednesday afternoon and into
Wednesday night. This enhanced LLJ will not only act to deliver
rich Gulf moisture northward, but it will also cause 850mb
frontogenesis to ensue over the Central Plains. PWATs will surge
to 1.8-2.0" within the Slight Risk area with MUCAPE ranging between
500-1,000 J/kg. These parameters would support up to 2.5"/hr
rainfall rates within storms that could contain mesocyclones. This
is due to vertical wind profiles that sport 30-40 knots of sfc-6km
shear and sfc-1 km SRH values in excess of 200 m/2 s/2.
Mesocyclones are efficient rainfall producers particularly in
environments with deep warm cloud layers and highly saturated
sfc-500mb environments, all of which apply in this situation. This
setup bears watching as locally significant flash flooding cannot
be ruled out.

...The West...

There remains no shortage of monsoon moisture throughout much of
the West, but the focus for flash flooding will become more
pronounced in the Northwest. An organized 700mb low will have an
abundance of moisture in place from OR/WA on east into the northern
Rockies. PWATs from the Blue Mountains and Snake River valley on
east across the Bitterroots and into southern MT/western WY are
likely to top the 99.5 climatological percentile and the presence
of the 700mb low will provide additional synoptic-scale support. In
addition, modest instability for the region will be present with
the ECMWF-EFI showing a pronounced signal for unusually high CAPE
(or instability) values across the northern Great Basin, eastern
OR, and much of ID. The same tool (ECMWF-EFI) depicts an impressive
QPF footprint over much of southern ID and even as far east as
southern WY. There was some contemplation of a Slight Risk for
parts of the Northwest tonight, however the region does need those
modest instability values (500-1,000 J/kg MUCAPE) to be realized in
order to increase the flash flood threat. Given there is still
some spread in where the heaviest QPF occurs and where the greatest
instability ensues, opted to hold off on a Slight Risk at this
time. However, should confidence increase in a more unstable
atmosphere come to fruition, a Slight Risk may be necessary in
future forecast cycles.

Mullinax
$$
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FOUS30 KWBC 270801
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
401 AM EDT Wed Aug 27 2025

Day 1
Valid 12Z Wed Aug 27 2025 - 12Z Thu Aug 28 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL PLAINS & NORTHWEST...

...Central Plains...

A sheared 500mb vort max exiting the Central Rockies will spawn a
surface low over the southern High Plains today. Working in tandem
with a dome of high pressure to the east, this will tighten the
pressure gradient and prompt a strengthening LLJ to form over the
Southern Plains late Wednesday afternoon and into Wednesday night.
This enhanced LLJ will not only act to deliver rich Gulf moisture
northward, but it will also cause 850mb frontogenesis to ensue over
the Central Plains. PWATs will surge to 1.8-2.0" within the Slight
Risk area with MUCAPE ranging between 500-1,000 J/kg. These
parameters would support up to 2.5"/hr rainfall rates within storms
that could contain mesocyclones. This is due to vertical wind
profiles that sport 30-40 knots of sfc-6km shear and sfc-1 km SRH
values in excess of 200 m/2 s/2. These vertical wind shear values
support mesocyclone formation, which are efficient rainfall
producers within environments containing deep warm cloud layers and
highly saturated sfc-500mb environments, all of which apply in
this situation. The latest 00Z HREF has started to show some higher
confidence in southeast KS in being the epicenter of the heaviest
rainfall. 24-hr QPF probabilities for >3" of rainfall are high
(70-90%) and probabilities for >5" are now 30-45%. While confidence
in locally significant rainfall amounts are increasing, the
placement still remains lower in confidence. With the bulk of this
event unfolding between 06-12Z Thurs, opted to hold off on a
categorical risk upgrade tonight to see if new 12Z HREF guidance
provides more supportive insight into the Wednesday night flash flood setup.

Meanwhile the Slight Risk area in the Central High Plains and along
the Front Range of the Rockies remains in place. Many locations now
sport overly saturated soils, as shown by the NASA SPoRT-LIS 0-40cm
soil percentiles which are above the 90th percentile. PWATs remain
above the 90th climatological percentile and anywhere from
500-1,000 J/kg of MUCAPE will provide sufficient instability to
support up to 1.5"/hr rainfall rates along the Front Range, and
perhaps as high as 2"/hr in the CO High Plains. The Slight Risk
remains in place due to the combination of anomalous moisture and
modest instability triggering storms over areas that feature
sensitive soils.

...The West...

There remains no shortage of monsoon moisture throughout much of
the West, but the focus for flash flooding will become more
pronounced in the Northwest. An organized 700mb low will have an
abundance of moisture in place from OR/WA on east into the northern
Rockies. PWATs from the Blue Mountains and Snake River valley on
east across the Bitterroots and into southern MT/western WY are
likely to top the 99.5 climatological percentile and the presence
of the 700mb low will provide additional synoptic-scale support. In
addition, modest instability for the region will be present with
the ECMWF-EFI showing a pronounced signal for unusually high CAPE
(or instability) values across the northern Great Basin, eastern
OR, and much of ID. The same tool (ECMWF-EFI) depicts an impressive
QPF footprint over much of eastern OR, southern ID, northern NV,
and into much of WY. Sufficient instability (500-1,000 J/kg
MUCAPE) is also present for storms to tap into from the northern
Great Basin on north into the Northern Rockies to justify rainfall
rates that approach 1.5"/hr. The Slight Risk remains on track given the forecast remains largely unchanged, and thus provides additional confidence
in the flash flood potential in the Bitterroots, Tetons, and Snake
River Valley today and into this evening.

Mullinax


Day 2
Valid 12Z Thu Aug 28 2025 - 12Z Fri Aug 29 2025

...THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL PLAINS, CENTRAL ROCKIES, & LOWER MISSISSIPPI VALLEY...

...Central Plains & Lower Mississippi Valley...

A 500mb vorticity maximum tracking towards the Ozarks on Thursday
will work with the diffluent right-entrance region of a 250mb jet
streak to provide excellent upper-level ascent over the Lower
Mississippi Valley. Further supporting the synoptic-scale forcing
over the Southern Plains and Lower Mississippi Valley is the
GFS/ECMWF showing 700mb Q-vector convergence over the region. This
is all occurring in the same area where low-level WAA is occurring
amidst WSW flow into a warm front that will meander around the
ArkLaTex on Thursday morning. This WAA will also usher in rich Gulf
moisture into the region that increases PWATs to 2.0-2.25"
throughout the Southern Plains and Lower Mississippi Valley. There
is also no shortage of instability, highlighted by a plume of
1,000-2,000 J/kg of MLCAPE for storms to work with. Given these
parameters, maximum rainfall rates could range between 2.5-3.0"/hr
within the most intense thunderstorms. These storms will also have
sufficient vertical wind shear (35-45 kts) and low-level SRH above
200 m2/s2, fostering mesocyclones within some thunderstorms just
north and east of the warm front. All these factors support the
potential for flash flooding within the Slight Risk area. Aside
from minor tweaks based off latest WPC QPF trends, no significant
adjustments were made this forecast cycle.

...Intermountain West...

A large pool of monsoonal moisture remains anchored over the
Rockies and Great Basin, highlighted by PWATs that are routinely
above the 90th climatological percentile in these regions. The
Northern Rockies will still have the lingering 700mb low over the
region that helps provide modest upper-level ascent to support
developing thunderstorms. Farther south, the Central Rockies are
located at the nose of a 250mb jet streak and low-level convergence
along the Front Range will foster widespread thunderstorms. Soils
will continue to saturate further in the days leading up to
Thursday over the Northern and Central Rockies that will further
exacerbate the flash flood threat. A Slight Risk is in place over
the Central Rockies that spills over into the the central High
Plains given the higher PWATs and instability in the region,
coupled with the gradually moistening soils. Given the lingering
spread in guidance regarding the placement of the strongest
thunderstorms, a Slight Risk was not issued as of this forecast
cycle. Should confidence increase in both heavier totals and
placement, and should antecedent soil moisture conditions continue
to grow more sensitive following Wednesday's rainfall, a
categorical risk upgrade may be necessary.

Mullinax


Day 3
Valid 12Z Fri Aug 29 2025 - 12Z Sat Aug 30 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER A LARGE
PORTION OF THE GREAT PLAINS, THE FRONT RANGE OF THE ROCKIES, AND
ACROSS MUCH OF THE DEEP SOUTH...

A pool of anomalous atmospheric moisture will maintain a
stronghold over the Northern Rockies and Plains on south through
the Southern Plains. A series of 500mb disturbances exiting the
Great Basin will provide some upper-level support for thunderstorms
from the northern Rockies and Plains on south to the Central
Rockies Front Range and Plains. Farther south, a nearby frontal
boundary in the southern High Plains will be the primary trigger
for thunderstorms. This area will have a greater concentration of
PWATs to work with (1.3-1.5" in the TX/OK Panhandles into eastern
NM) and greater MLCAPE values (topping 1,000 J/kg). These areas
will have seen soils dry up following a couple days of drier
weather, and given some global guidance members differ on the
location of the storms, there was no categorical risk upgrade this
forecast cycle.

Farther east, a wave of low pressure will track east along a
frontal boundary that stretches from the Front Range of the
Rockies to Florida. Numerous showers and thunderstorms are likely
to envelope the South, with the Lower Mississippi Valley favored to
see the heaviest rainfall at this time. Guidance shows the Lower
Mississippi Valley sporting the highest PWATs (2.0-2.25") and
instability (MLCAPE 1,000-2,000 J/kg) while also being more
favorably located closer to the emerging area of low pressure in
eastern TX. The GEFS/GEPS camps favor the Lower Mississippi Valley,
but many ECMWF members were still showing storms that could
produce locally heavy rainfall as far east as eastern GA. Given the
lingering spread in model guidance, and the Lower Mississippi
Valley's currently higher 1-3hr FFG exceedance values, there was no
categorical risk upgrade hoisted as of this forecast cycle. But
the >2.0" PWATs and modest instability does support a localized
flash flood threat across much of the South during a time that also
just so happens to be the kickoff to Labor Day weekend. Flash
flooding could result in some locally hazardous travel conditions,
especially along roads that drain poorly.

Mullinax
$$
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FOUS30 KWBC 280825
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
425 AM EDT Thu Aug 28 2025

Day 1 Valid 12Z Thu Aug 28 2025 - 12Z Fri Aug 29 2025

...THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL ROCKIES AND THE SOUTHERN PLAINS INTO THE LOWER
MISSISSIPPI VALLEY...

...Southern Plains into the Lower MS Valley...
Convection will be ongoing at 12z this morning across portions of
southeast KS, northeast OK and into central and northern AR. Some
northwest to southeast training of convection is expected, and
scattered instances of flash flooding will probably be ongoing and
continue into the morning hours. Instability is a limiting factor,
and interesting to note that the 05z HRRR has significantly less
CAPE at 12z than the 00z HRRR and other 00z HREF members. This
downward trend in instability during the morning hours should
limit the coverage and magnitude of the flash flood risk from
eastern OK into AR...however convection should still train enough
to produce isolated to scattered flash flooding, especially over
any more susceptible areas, with amounts of 2-4" still probable.

By later this morning into the afternoon hours indications are
that convection should begin to forward propagate off to the south,
picking up speed as it pushes into and through southern AR.
Instability should be on the increase by this time resulting in
higher rainfall rate potential, but the expected quicker cell
motions should still cap the flash flood risk in the isolated to
scattered range.

Another uptick in convection is likely Thursday night into Friday
morning as low level convergence increases. More uncertainty with
the details by this time, but an area of expanding backbuilding
convection could develop over the ArkLaTex during this timeframe,
potentially driving and increased flash flood risk.

Model QPF forecasts are getting to the level of MDT risk
consideration. However do note that HREF probabilities of exceeding
3hr FFG do not get much above 25%, and probabilities of this
magnitude are not widespread. Typically we see higher HREF FFG
exceedance probabilities in MDT risk level events. The high FFG
over much of the area is likely the primary driver of these lower probabilities, however the aforementioned lower instability in
place this morning is also likely to keep rainfall rates a bit
lower and thus less likely to exceed FFG on a more
numerous/widespread basis. Nonetheless will need to continue to
closely monitor model/observational trends today. At the moment,
the activity tonight into Friday morning over the ArkLaTex seems to
have the better chance of reaching MDT risk levels, especially if
rainfall this afternoon is able to lower FFG ahead of what should
be an uptick in backbuilding/training tonight into Friday morning.
Not enough confidence in the details to go MDT, but still think
higher end Slight risk probabilities are justified across portions
of eastern OK into western AR, far northeast TX and far northwest LA.

...Rockies and Western U.S....
A small Slight risk was maintained across portions of southeast
CO. With easterly upslope flow into the Front Range high res models
indicate convective initiation this afternoon, with cells moving
eastward into the CO Plains, before diving off to the south. Some
initial slow cell motions and the possibility of a cell merger or
two will allow for areas of locally heavy rainfall. Most models
really only indicate one or two stronger cells persisting long
enough to drive a flash flood risk...so there is a question whether
the coverage of flash flooding will reach Slight risk levels. But
given the risk is already out, and the fact that models continue
to show a focus for heavier rainfall amounts over this corridor, we
opted to maintain the Slight risk.

Elsewhere a broad Marginal risk covers much of the Intermountain
West. Not expecting as much coverage of convection or as heavy of
rainfall totals as we saw on Wednesday, but localized areas of
heavy rainfall remain possible within the Marginal risk area. The
best convective focus will likely be across portions of
southern/central MT and northeast WY, but only modest instability
should keep rainfall rates down enough to keep any flash flood
risk isolated in nature.

Chenard


Day 2 Valid 12Z Fri Aug 29 2025 - 12Z Sat Aug 30 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER EASTERN NEW
MEXICO INTO THE TEXAS PANHANDLE, AND OVER PORTIONS OF THE LOWER
MISSISSIPPI VALLEY AND SOUTHEAST...

...Lower MS Valley into the Southeast...
The mesoscale and synoptic features responsible for the day 1
convection over the Southern Plains and Lower MS Valley will shift
southeast on Friday. More model spread is noted by this
time...with the 00z GFS remaining an outlier. The GFS continues to
be more suppressed and weaker with this feature than the other
global model guidance. The ECMWF, CMC, UKMET, ICON and NAM are all
farther northeast with the heavy rainfall axis stretching into
portions of MS and AL than the GFS is. The AIFS and both the ECMWF
and GFS initialized Graphcast are also farther northeast than the
GFS. Thus, it seems more likely than not that the GFS is too
suppressed and it represents a less likely outcome at the moment.
The ECMWF has been the most aggressive with a farther northeast
axis, but do note that is has been gradually trending southwest the
last few runs...and so the ECMWF may be a bit too far northeast.

Given the above model diag, it seems prudent to go ahead with a
Slight risk across portions of the region. The environmental
ingredients will be conducive to heavy rainfall, with PWs over 2"
and a corridor of persistent lower level moisture
transport/convergence supporting some backbuilding and/or training
potential. Other than the weaker GFS, models show an area of low
pressure only slowly moving eastward along a low level frontal
axis...with upwards of 2000 j/kg of CAPE near and south of this
boundary. Thus it does seem like an excessive rainfall threat
could evolve Friday into Friday night with either a persistent
swath of convection or multiple convective rounds. The Slight risk
area was drawn from portions of central/northern LA into
central/southern MS and southwest AL...as this corridor is
generally the consensus axis of heaviest rainfall potential from
the non-GFS solutions. The high FFG keep this as just a lower end
Slight risk for now, and I would expect to see some adjusting of
the risk area as we get closer and models better converge on a solution.

...Rockies into the High Plains...
A Slight risk was also added for eastern NM into the TX Panhandle.
We should see an uptick in both CAPE and PW compared to Thursday,
and a shortwave feature and upper jet on the northern periphery of
the upper level ridging will help initiate convection Friday
afternoon. It also looks like some mid/upper level moisture
streaming well north and east of Juliette in the Eastern Pacific
will move into these areas Friday, likely helping increase rainfall
efficiency. High res models indicate convection initiating over
eastern NM near higher terrain Friday afternoon, before propagating
off to the east. Cell motions look rather quick off to the east,
which may end up limiting the extent/magnitude of the flash flood
risk. However it looks like enough of a surge in instability and
PWs to suggest high rainfall rates, and we could be looking at
enough convective coverage to support some upscale convective
cluster development. So there seems to be enough there to justify
going with a Slight risk over these areas.

Elsewhere, areas of convection across portions of NE into SD and
MT will pose a localized flash flood risk. Convective coverage and
intensity here also looks higher than Thursday, and can not rule
out eventually needing another targeted slight risk area, but for
now even with the greater convective coverage, any FFG exceedance
looks isolated in nature.

Chenard


Day 3 Valid 12Z Sat Aug 30 2025 - 12Z Sun Aug 31 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM EASTERN NEW
MEXICO INTO WEST TEXAS...

...Rockies into the Plains...
Mid/upper level riding will gradually breakdown by Saturday over
the Plains resulting in increased troughing and embedded shortwave
energy. This should drive rather widespread convection from TX/NM
all the way into the Dakotas. A Slight risk was maintained from
eastern NM into the TX Panhandle and west central TX where the
ingredients appear better for an excessive rainfall threat. This
area will see an uptick in instability compared to Friday, with
PWs also trending slightly higher and well within the range of
supporting heavy rainfall rates. The right entrance region of an
upper jet and an increase in low level moisture transport Saturday
evening support an organized convective threat. Convective details
this far out are uncertain, but the overall pattern supports
terrain driven convection over NM growing upscale as it moves
eastward into western TX resulting in an isolated to scattered
flash flood threat.

...Southeast...
More uncertainty exists over the Southeast by Saturday. As was
described in the day 2 discussion, still think the 00z GFS is an
outlier and lower probability solution. Most other models indicate
a lingering frontal boundary with a low and enhanced moisture
transport. Thus it seems more likely than not that at least
localized areas of heavy rainfall will remain possible from the
Gulf Coast and possibly into portions of GA and SC. The northern
extent of this risk is more uncertain, and quite possible the 00z
ECMWF (and other recent ECMWF runs) is too far north and east. But
somewhere from the central Gulf Coast into north FL and southern
GA still looks in play for heavy rainfall Saturday into Saturday
night. The overall environmental ingredients would support Slight
risk level rainfall...however the combination of high FFG and
above average uncertainty suggests sticking with a broad Marginal
risk is the best course of action for now.

Chenard
$$
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FOUS30 KWBC 290820
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
420 AM EDT Fri Aug 29 2025

Day 1
Valid 12Z Fri Aug 29 2025 - 12Z Sat Aug 30 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER EASTERN NEW
MEXICO INTO THE TEXAS PANHANDLE, THE NORTHERN/CENTRAL PLAINS, AND
OVER PORTIONS OF THE LOWER MISSISSIPPI VALLEY AND SOUTHEAST...

...Lower MS Valley into the Southeast...

Conditions will be favorable across the Lower Mississippi
Valley/Gulf states for convection to backbuild and/or train. PW
values around 2 inches will be pooled over the region as an area of
low pressure slowly propagate along a frontal boundary.
Considering the environmental factors and deep layer ascent, there
will surely be areas that see > inches of rainfall during the
forecast setup with modest neighborhood probabilities for >5 inches
(20-35%) situated across the aforementioned areas. Higher FFG's
will curb the top end of any threat as the recent dry pattern has
relegated all 1/3/6 indices to run very high, a state that usually
leaves significant flash flood potential muted historically. The
Slight Risk will likely be a low end threat and spans from far
eastern Texas to central Alabama.

...Rockies into the High Plains...

A shortwave feature and upper jet on the northern periphery of
the upper level ridging will help initiate convection during the afternoon.
It also looks like some mid/upper level moisture streaming well
north and east of Juliette in the Eastern Pacific will move into
these areas, likely helping increase rainfall efficiency.
Hi-res solutions continue to depict convective initiation near the
higher terrain of eastern New Mexico during the afternoon hours
before progressing swiftly eastward during the evening and
overnight hours; this may limit the magnitude of the flash flood
risk. However it looks like enough of a surge in instability and
PWs to suggest high rainfall rates, and we could be looking at
enough convective coverage to support some upscale convective
cluster development. The Slight Risk area was maintained with minor
reshaping to reflect the latest trends and WPC QPF.

Further north, areas of convection across portions of
Nebraska, South Dakota and Montana will pose a localized flash
flood risk. Guidance continues to focus the greatest amounts from
south-central South Dakota to southern Nebraska, noting an uptick
in activity and amounts from previous runs. A Slight Risk was
raised for an increased threat for localized flooding concerns.

...Northeast...

Convection along a slow advancing frontal has the potential to
produce very localized 1-3 inches along the I-95 corridor, with
the greater potential focusing across portions of New Hampshire and
Maine. A Marginal Risk area was raised from eastern
Connecticut/Rhode Island north/northeastward to central Maine.

Campbell/Kleebauer/Chenard


Day 2
Valid 12Z Sat Aug 30 2025 - 12Z Sun Aug 31 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM EASTERN NEW
MEXICO INTO WEST TEXAS AND ACROSS THE PLAINS...

...Southeast...

During this period convection will focus near a lingering frontal
boundary with a surface low and enhanced moisture transport. Thus
it seems more likely than not that at least localized areas of
heavy rainfall will remain possible from the Gulf Coast and
possibly into portions of Georgia and South Carolina. The best
threat would be for urban areas since local FFG are high across the
region. The northern bounds of the Marginal Risk was lifted
northward to include more of central Georgia.

...Rockies into the Plains...

Increased troughing and embedded shortwave energy is expected
during this period as the upper level ridging breaks down. This
may result in widespread convection to develop and spread out
across the Plains. The Slight risk was maintained from eastern New
Mexico into the Texas Panhandle and west-central Texas where the
alignment of increased instability and higher PW values are better
for an excessive rainfall threat. The right entrance region of an
upper jet and an increase in low level moisture transport Saturday
evening support an organized convective threat. This pattern
supports terrain driven convection over New Mexico growing upscale
as it moves eastward into western Texas resulting in an isolated to
scattered flash flood threat. The Slight Risk that was already in
place was maintained with only a minor expansion of the eastern
bounds over central Texas.

A Slight Risk was raised for this period parts of South Dakota,
Nebraska and Kansas as the area of convection in the Day 1 period
advances eastward along and ahead of the propagating front. Much
of the guidance show areal averages of 1 to 3 inches with local
maxes of 4+ possible.

Campbell/Chenard


Day 3
Valid 12Z Sun Aug 31 2025 - 12Z Mon Sep 01 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM SOUTHERN NEW
MEXICO INTO WEST TEXAS...

Heavy rainfall will continue to focus along a draped frontal
boundary from the Southern Plains to the South East. The moist
monsoonal flow along with embedded shortwave energies traversing
the flow will help enhance rainfall amounts, particularly over
southern New Mexico and West Texas where a Slight Risk for
excessive rain persist. A broad Marginal Risk spans from eastern
Arizona to the Southeast Coast.

Convection ahead of the front in the Plains will continue to pose
an elevated threat for excessive rainfall. A Marginal Risk was
carried over from yesterday's Day 4 period.


Campbell
$$
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FOUS30 KWBC 300805
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
405 AM EDT Sat Aug 30 2025

Day 1
Valid 12Z Sat Aug 30 2025 - 12Z Sun Aug 31 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM EASTERN NEW
MEXICO INTO WEST TEXAS AND ACROSS THE PLAINS...

...Rockies into the Plains...

Increased troughing and embedded shortwave energy is expected
during this period as the upper level ridging breaks down. This
may result in widespread convection to develop and spread out
across the Plains. An axis of high QPF values is expected to set up
from far eastern New Mexico east towards the Dallas/Fort Worth
area, which will be the area with the highest potential for flash
flooding, especially near steep terrain and burn scars. This
pattern supports terrain driven convection over New Mexico growing
upscale as it moves eastward into western Texas resulting in an
isolated to scattered flash flood threat.The Slight Risk area was
maintained for this part of the region. Elsewhere, the broad
Marginal was maintained across much of the Plains and for portions
of the Gulf Coast and Southeast. There was an uptick in QPF amounts
and coverage across portions of eastern Texas which warranted an
eastern nudge of the Marginal Risk.

The Slight Risk area across the Plains was expanded eastward into
eastern Kansas and far northern Oklahoma, which was supported by
hi- res CAM QPF, high HREF probabilities for rain rates exceeding 1
inch per hour and 2 inches per 6 hours, and moderate HREF
probabilities for 24 hour QPF exceeding 5-year ARIs. The latest
guidance depicted a southern shift and reduction in threat of
excessive rainfall for parts of South Dakota and northern Nebraska,
therefore the northern bounds of the Slight Risk was trimmed down
to eastern Nebraska. Within this Slight Risk area, the high end
potential is expected to focus over eastern Nebraska, where this
will likely become more of a long duration event with high rain
rates in individual storms.

Campbell/Dolan


Day 2
Valid 12Z Sun Aug 31 2025 - 12Z Mon Sep 01 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM SOUTHERN NEW
MEXICO INTO WEST/CENTRAL TEXAS AND FOR EASTERN NEBRASKA...

Convection over eastern Nebraska and Kansas will likely see enough
instability and moisture to support high rain rates. Soils in this
region should also be saturated from heavy rain/storms expected on
Saturday, resulting in a heightened flash flood risk. The inherited
Slight Risk was expanded south and east to cover more of eastern Kansas.

The Slight Risk area in Texas was also expanded to include more of
eastern Texas and far southeast Arizona. This was to account for
an increasing trend in QPF and the potential for repeat
thunderstorm activity over areas that will be saturated by storms.
The better focus for higher QPF will be for locations near or east
of the Hill Country across eastern Texas.

The broader Marginal Risk areas for the southern tier and portions
of the Central/Northern Plains continue to highlight the level
threat for excessive rainfall and flooding potential across the region.

Campbell


Day 3
Valid 12Z Mon Sep 01 2025 - 12Z Tue Sep 02 2025

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR THE SOUTHERN
TIER, PLAINS AND TENNESSEE VALLEY...

A surface front will continue to be draped across the southern
tier of the country providing a focus for the monsoonal moisture
and Gulf moisture. There will be some upper level support for
isolated convection therefore the Marginal Risk was maintained from
New Mexico and southeast Arizona across southern/central parts of
Texas and the Gulf Coast through the Florida Peninsula.

To the north, a frontal system and a shortwave or two aloft will
support storms with higher rain rates across the Mid-Mississippi
Valley and the Tennessee Valley to Southern Appalachians.
Maintained the Marginal Risk areas for the Tennessee Valley and for
the Plains.

Campbell
$$
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FOUS30 KWBC 310805
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
405 AM EDT Sun Aug 31 2025

Day 1
Valid 12Z Sun Aug 31 2025 - 12Z Mon Sep 01 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM SOUTHERN NEW
MEXICO INTO WEST/CENTRAL TEXAS AND FOR EASTERN NEBRASKA...

Abundant instability and moisture influx will help maintain
convection over the Plains. High rain rates combined with nearly
saturated soils from recent heavy rain/storms will keep an elevated
threat for flash flooding for the region. A Slight Risk clips far
southeast South Dakota, eastern Nebraska, eastern Kansas, northwest
Missouri and western Iowa.

Easterly flow will allow storms that develop over the Gulf to move
into the coastal areas of Texas and western Louisiana. Meanwhile
the stalled frontal boundary over the area will continue to provide
forcing into the rest of Texas and New Mexico. For many areas, dry
clay soils will allow for most of the rainfall in the typically
dry desert areas to convert to runoff quickly. The better focus
for higher QPF will be for locations near or east of the Hill
Country across eastern Texas. A Slight Risk spans from southeast
Arizona to the southeast coast of Texas within a broader Marginal
Risk for the southern tier and portions of the Central/Northern Plains.

Campbell


Day 2
Valid 12Z Mon Sep 01 2025 - 12Z Tue Sep 02 2025

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR THE
SOUTHERN TIER, PLAINS AND TENNESSEE VALLEY...

A frontal system and a shortwave or two aloft will support storms
with higher rain rates across the Lower Missouri/Mid-Mississippi
Valley and the Tennessee Valley to Southern Appalachians. The
Marginal Risk areas for the Tennessee Valley and for the Plains
remain in effect for this period.

The stalled frontal boundary along the Gulf Coast and into Texas is
expected to advance a little southward during this period leading
to the QPF footprint being offset from prior days which will limit
the flooding potential. The heaviest rain is still expected to
focus along the I-10 corridor from Houston to San Antonio and may
still cause impacts. A broad Marginal Risk remains in effect from
the Southwest, southern Texas/western Gulf coastline an much of the
Florida peninsula.

Campbell


Day 3
Valid 12Z Tue Sep 02 2025 - 12Z Wed Sep 03 2025

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHWEST/CALIFORNIA, FLORIDA, LOWER MISSISSIPPI/TENNESSEE
VALLEYS AND THE UPPER MIDWEST...

A Marginal Risk area was maintained for the Mid-South as shortwave
energy and a weak low traversing the cold front may trigger
convection capable of higher rainfall rates over the region.
Meandering frontal boundaries within an unstable environment will
support heavy rainfall and localized flash flooding potential for
Florida, therefore the Marginal Risk area was kept for this period.

A cold front will drop into the Northern Plains and Upper Midwest
ahead of the strong reinforcing upper trough. Convection is
expected fire up along and ahead of the frontal boundary, with
potential for heavy rainfall. A Marginal Risk area is in effect for
the eastern Dakotas, northern Iowa, Minnesota, northern Wisconsin,
and portions of the UP of Michigan.

Meanwhile, monsoonal moisture is forecast to flow into the
southwestern U.S. underneath the mean upper ridge for scattered
showers and thunderstorms. A Marginal Risk span from southern
Colorado/New Mexico westward to eastern California.

Campbell
$$
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FOUS30 KWBC 010753
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
353 AM EDT Mon Sep 1 2025

Day 1
Valid 12Z Mon Sep 01 2025 - 12Z Tue Sep 02 2025

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN TIER, PLAINS, EAST COAST OF FLORIDA, AND TENNESSEE
VALLEY...

The stalled frontal system and monsoonal moisture will persist
across southern Arizona, New Mexico, and Texas. Isolated convection
across the region expected, keeping the threat for flash to
isolated instances. A Marginal Risk remains in effect for portions
of Arizona, New Mexico, and western/southern Texas.

Easterly onshore flow into Florida warrants maintaining a Marginal
Risk for the eastern coastal areas.

Antecedent dry conditions along the Appalachians should preclude
any flash flooding. Better coverage of convection should stay
further west into central Tennessee and northern Alabama. A vort
max tracking east across Tennessee will be the forcing mechanism
for any convection across Middle Tennessee. A Marginal Risk was the
appropriate threat level for this period.

Finally, the Marginal in the Plains was reshaped to a slightly more
SW-NE orientation rather than mostly N-S. Instability and abundant
cloud cover should limit the flooding threat, but prior rains from
previous days in the form of more saturated soils could support an
isolated flash flooding risk.

Campbell/Wegman


Day 2
Valid 12Z Tue Sep 02 2025 - 12Z Wed Sep 03 2025

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE MIDDLE TENNESSEE VALLEY...

Remnant convection from the overnight period on Monday night will
persist into Tuesday as a reinforcing shortwave digs southward and
reaches Middle Tennessee by Tuesday night. A weak, but still
significant low level jet will advect Gulf moisture northeastward
across the Deep South and into Tennessee on Tuesday, which will
keep a steady supply of fuel in place for any convection. Thus,
expect a long-duration rain event, that while much of it will be
light, the LLJ advecting moisture into Tennessee and various
different sources of forcing will support some storms becoming
strong and able to produce heavy rain. The storms will also be
slow-moving, which will lengthen the amount of time any area sees
heavy rain. A Slight remains in effect for portions of Mississippi,
Alabama, and Tennessee.

A cold front will drop into the Northern Plains and Upper Midwest
ahead of the strong reinforcing upper trough. Convection is
expected fire up along and ahead of the frontal boundary, with
potential for heavy rainfall. A Marginal Risk area is in effect for
the eastern Dakotas, northern Iowa, Minnesota, northern Wisconsin,
and portions of the UP of Michigan.

The stalled out front across Florida will support more widespread
convection Tuesday afternoon across much of the Peninsula, while
the Panhandle dries out a bit from prior days' rains. A second
shortwave and associated front will produce areas of heavy rain
across portions of the upper Midwest. A Marginal Risk remains in
effect for most of central and southern portions of the Peninsula.

Monsoonal moisture is forecast to flow into the southwestern U.S.
underneath the mean upper ridge notably shifted a bit westward for
this period. Scattered convection expected across the region and
is covered by a Marginal Risk spanning from eastern California,
Arizona, New Mexico and into southern Colorado.

Campbell/Wegman


Day 3
Valid 12Z Wed Sep 03 2025 - 12Z Thu Sep 04 2025

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PARTS OF THE
SOUTHWEST, FLORIDA, AND THE UPPER GREAT LAKES/UPPER MIDWEST...

Deep moisture along the stalled frontal boundary will continue to
generate convection capable of producing heavy rain across the
Florida Peninsula. A Marginal Risk is in effect for most of
central and southern portions of the state. Meanwhile, monsoonal
moisture and diurnal heating will continue to trigger convection
across the West/Southwest maintaining an elevated threat for
isolated flash flooding for vulnerable locations. A Marginal Risk
is in effect from New Mexico to eastern California. Further north,
heavy rainfall is expected across portions of the Upper
Midwest/Upper Great Lakes as the frontal boundary continues to
advance eastward. A Marginal Risk encompasses portions of Wisconsin
and northern Michigan.


Campbell
$$
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FOUS30 KWBC 020818
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
418 AM EDT Tue Sep 2 2025

Day 1
Valid 12Z Tue Sep 02 2025 - 12Z Wed Sep 03 2025

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHERN CALIFORNIA AND SOUTHERN ARIZONA...

...Southwest...

There will be a nearly continuous anomalous surge in monsoonal
moisture into the Sierra Nevada due to the position of the upper
ridge axis to the east and a weak upper low along the central
California coast to the west. PW anomalies of 2 to 3 sigma are
forecast from the lower Colorado River up trough the Sierra Nevada
and even into southern Oregon by 00Z Wed. Impressive CAPE will also
be present across southern Arizona and southern California, showing
support for heavy rainfall especially over flashy prone areas.
This environment has the potential for more than just isolated
areas of flash flooding, therefore a Slight Risks were raised for
southern Arizona and southern California.

...Mid-South through Tennessee Valley...

Remnant boundaries from ongoing convection today combined with
additional lift from a digging trough from the central U.S. should
allow convective activity to be in similar areas (and west) from
yesterday's coverage. However, moisture is limited to around 1.5".
This uptick will allow for some greater rates and motion should
remain slow overall, but overall the rainfall magnitude continues a
decreasing trend. A Marginal Risk remains in effect from central
Mississippi to Kentucky.

...Upper Midwest...

During this period a cold front is expected to traverse across the
Dakotas and encounter pooled moisture with a PW of 1.25", which is
1 sigma above normal. Diurnally enhanced convection is expected
fire up along and ahead of the frontal boundary and will have the
potential to produce heavy rainfall for Minnesota, northern Iowa,
Wisconsin and the U.P. of Michigan. A Marginal Risk was kept for this area.

Campbell/Jackson


Day 2
Valid 12Z Wed Sep 03 2025 - 12Z Thu Sep 04 2025

...THERE IS A SLIGHT RISK FOR PORTIONS OF SOUTHERN CALIFORNIA AND
SOUTHER ARIZONA...

...Southwest...

Anomalous monsoonal moisture will continue to affect northward
from the lower Colorado Valley through the Sierra Nevada and much
of Nevada. Diurnally- driven activity can be expected again over
the Sierra Nevada which may be locally excessive, as well as much
of Nevada through western Arizona and southwest Utah. A broad
Marginal Risk cover much of Arizona,southeast Utah, southern
Nevada, and eastern/southern California. The presence of strong
CAPE embedded with the deep column of moisture, especially across
southern Arizona and across the Transverse and Peninsular Ranges of
southern California will be conducive for heavy rainfall and
scattered areas of flash flooding. These locals will be vulnerable
to the high rainfall rates, especially in the flashy prone
locations. A Slight Risk was raised in coordination with the local
forecast offices.

...Central U.S...

Elevated moisture ahead of the strong cold front sweeping down the
Plains will trigger heavy rainfall again. Enough focus is present
to warrant maintenance of the Marginal Risk around the central
Great Lakes though timing is in question. While much of the
activity should be progressive, there is a repeating threat on the
southern end of activity along the southern Kansas/Missouri
border- a Marginal Risk was carried on for this period.

...Florida...

Enhanced rainfall expected to develop within the very moist airmass
along the stalled frontal boundary. Individuals cells will focus
heavy rainfall over the southern peninsula and the Keys thus
keeping an elevated threat for flash flooding.

Campbell


Day 3
Valid 12Z Thu Sep 04 2025 - 12Z Fri Sep 05 2025

...THERE IS A MARGINAL RISK AREA FOR PORTIONS OF FLORIDA,
SOUTHWEST/GREAT BASIN, AND THE NORTHEAST...

...Florida...

The environment will remain nearly the same as the Day 2 period,
thus convection will persist. Heavy rain will be possible therefore
the Marginal Risk was maintained southern Florida and expanded
southward to cover the Keys.

...Northeast...

The cold front passing through the Lower Great Lakes and into the
Northeast will be fairly progressive, however there are signals
for higher QPF to focus across central and northern portions of New
York. Parts of the region have been drier with some areas with
notable drought conditions, which will limit the potential for
impacts from heavy rainfall. The highest amounts are expected for
the more elevated locations which will increase the threat for
flooding concerns. A Marginal Risk area was maintained from the
previous Day 4 but with portions of western and eastern new York
trimmed out given the D0/D1 drought conditions.

...Southwest, California and southern Great Basin...

The monsoonal moisture will continue to advect into the
southwestern U.S. underneath the mean upper ridge, promoting
scattered showers and thunderstorms. Moisture anomalies are
expected to be the greatest for portions of California and Nevada.
A broad Marginal Risk encompasses eastern California, most of
Nevada, southeast Utah, Arizona and west/central New Mexico.

Campbell
$$
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FOUS30 KWBC 030850
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
450 AM EDT Wed Sep 3 2025

Day 1
Valid 12Z Wed Sep 03 2025 - 12Z Thu Sep 04 2025

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHERN ARIZONA...

...Southwest...
A broad area of instability and above normal moisture will bring a
localized flash flood risk to much of the southwestern U.S. today.
HREF guidance indicates the best convective coverage will be
across southern AZ where neighborhood probabilities of 2"+ amounts
are 30-50%. This generally looks to be where the better
instability is forecast today, and also where the heaviest rainfall
occurred yesterday. Thus maintaining the Slight risk across this
areas seems reasonable.

...South FL...
A wet pattern will persist over south FL through Friday with
localized flash flooding possible each day. The overall pattern
does not change too much, with a stationary front in the low
levels, an upper jet to the north providing some right entrance
region ascent, and broad mid level troughing. It seems likely that
rounds of convection will occur each day, and with PWs around 2.3",
heavy rainfall rates are likely. There is some uncertainty with
the axis of heaviest rainfall each day, with some models favoring
the Keys, and given the location of the stationary front, this may
make sense. However it still seems likely that heavier convection
will impact the urban corridor of southeast FL at times as well.
Uncertainty regarding both the axis and also the speed of
convection, whether it tends to propagate eastward quickly or can
hang up, dictates keeping the risk at Marginal for now. Although
could certainly see the need for a targeted Slight risk along the
southeast FL urban corridor at some point over the next 3 days
given the potential for multiple rounds of heavy rainfall.

Chenard

Day 2
Valid 12Z Thu Sep 04 2025 - 12Z Fri Sep 05 2025

...THERE IS A SLIGHT RISK FOR PORTIONS OF SOUTHEAST CALIFORNIA AND
CENTRAL AND SOUTHERN ARIZONA...

...Southwest...
Thursday is looking like a more active day across portions of AZ
into southeast CA as the area begins to feel the impacts of a
stronger moisture surge ahead of Lorena. An uptick in moisture and
low level flow should help drive a more organized convective
threat. Rather impressive instability for this part of the country
is forecast, with values upwards of 2000-3000 J/KG, and this
combination of above average PWs and instability should support
intense rainfall rates. Always worry about cloud cover impacting
instability, which could happen in spots, but the overall model
signal certainly favors areas of robust instability. In a part of
the country where model QPF struggles, CAPE and PW overlap often
ends up being a better flash flood potential indicator. Given the
ingredients in place, we went ahead and upgraded to a Slight risk
for much of central and southern AZ into southeast CA. Additional
expansion into more of southeast CA are possible going forward.

...South FL...
A wet pattern will persist over south FL through Friday with
localized flash flooding possible each day. The overall pattern
does not change too much, with a stationary front in the low
levels, an upper jet to the north providing some right entrance
region ascent, and broad mid level troughing. It seems likely that
rounds of convection will occur each day, and with PWs around 2.3",
heavy rainfall rates are likely. There is some uncertainty with
the axis of heaviest rainfall each day, with some models favoring
the Keys, and given the location of the stationary front this may
make sense. However it still seems likely that heavier convection
will impact the urban corridor of southeast FL at times as well.
Uncertainty regarding both the axis and also the speed of
convection, whether it tends to propagate eastward quickly or can
hang up, dictates keeping the risk at Marginal for now. Although
could certainly see the need for a targeted Slight risk along the
southeast FL urban corridor at some point over the next 3 days
given the potential for multiple rounds of heavy rainfall.

Chenard

Day 3
Valid 12Z Fri Sep 05 2025 - 12Z Sat Sep 06 2025

...THERE IS A MARGINAL RISK AREA FOR PORTIONS OF FLORIDA,
AND THE WESTERN U.S....

...Southwest...
More uncertainty with the flash flood forecast on Friday compared
to Thursday. The potential is there for more direct impacts from
Lorena across portions of AZ and NM, but confidence on the details
is low. The GFS, RRFS and GFS based hurricane model (HAFS) have
consistently been indicating a stronger system that is able to move
into northwest Mexico. This evolution would likely result in
strong enough low level forcing to drive convection and a flash
flood risk over portions of southeast AZ into southwest NM. However
the non-NCEP global models and the NAM suggest the low level
center of the system weakens and stays offshore Baja California,
with just the mid and upper level energy ejecting northeastward.
This would probably result in quite a bit of mid and upper level
moisture moving into AZ and NM, and while this could result in a
steady rainfall, the cloud cover would probably hinder
destabilization and keep rainfall rates and the flash flood risk
lower. So this could be a case where the areal averaged rainfall is
higher, but the flash flood risk is actually lower given the
decreased rates. Given this uncertainty we opted to stick with a
Marginal risk in the ERO despite our deterministic QPF showing
upwards of 1-2" of rain over southeast AZ into southwest NM. We
will continue to monitor trends and adjust as needed on future
updates.

Elsewhere across the West the large Marginal risk area stretches
northward into OR and as far east as CO. The overall synoptic
pattern favors isolated to scattered convection over this entire
area, and the forecast PWs and instability would support locally
heavy rainfall rates. At the moment not seeing enough coverage to
justify any Slight risk areas, but we will continue to monitor.
Sometimes we can get a more organized flash flood risk develop on
the edge of the deeper tropical moisture, where cloud cover is low
enough to allow for destabilization, but moisture is still high
enough for heavy rates.

...South FL...
A wet pattern will persist over south FL through Friday with
localized flash flooding possible each day. The overall pattern
does not change too much, with a stationary front in the low
levels, an upper jet to the north providing some right entrance
region ascent, and broad mid level troughing. It seems likely that
rounds of convection will occur each day, and with PWs around 2.3",
heavy rainfall rates are likely. There is some uncertainty with
the axis of heaviest rainfall each day, with some models favoring
the Keys, and given the location of the stationary front this may
make sense. However it still seems likely that heavier convection
will impact the urban corridor of southeast FL at times as well.
Uncertainty regarding both the axis and also the speed of
convection, whether it tends to propagate eastward quickly or can
hang up, dictates keeping the risk at Marginal for now. Although
could certainly see the need for a targeted Slight risk along the
southeast FL urban corridor at some point over the next 3 days
given the potential for multiple rounds of heavy rainfall.

The large scale pattern becomes more meridional by Friday, with
upper level flow becoming more southerly over south FL and the
upper jet orientation favoring a bit more upper level divergence.
Thus could potentially see a pattern that may favor more of a
stationary or training convective threat along the urban corridor
of southeast FL. However the location of the front by then will
play a role in this, and so not confident enough to go with a
Slight risk at this point.

Chenard
$$
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FOUS30 KWBC 040849
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
449 AM EDT Thu Sep 4 2025

Day 1
Valid 12Z Thu Sep 04 2025 - 12Z Fri Sep 05 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHEAST CALIFORNIA AND CENTRAL AND SOUTHERN ARIZONA...

...Southwest...

The signal is clear within all CAMs leading to a strong
probability assessment for 3 and 6hr FFG exceedance intervals, each
carrying 50+% over a large area extending from Tuscon all the way
to the Colorado River basin between the 18-06z time frame in the
period. Rates of 1-2"/hr will be plausible in this setup as PWATs
remain ~2 deviations above normal, a signal favoring locally heavy
rainfall and heightened flash flood concerns over flashy
soil/terrain features. Rather impressive instability for this part
of the country is forecast, with values upwards of 2000-3000 J/KG,
and this combination of above average PWs and instability should
support intense rainfall rates. Always worry about cloud cover
impacting instability, which could happen in spots, but the overall
model signal certainly favors areas of robust instability. In a
part of the country where model QPF struggles, CAPE and PW overlap
often ends up being a better flash flood potential indicator. A
Slight risk for much of central and southern Arizona into southeast
California was maintained for this period.

...South Florida...

A persistent wet pattern to continue through the weekend thanks to
stationary front in the low levels, an upper jet to the north
providing some right entrance region ascent, and broad mid level
troughing. Rounds of convection will occur each day, and with PWs
around 2.3", heavy rainfall rates are likely. The exact location
of the axis of heaviest rainfall is a bit uncertain, but most of
the guidance is favoring the Keys and southern portions of the
peninsula. Heavier convection may impact the urban corridor of
southeast Florida at times as well. A Marginal Risk area remains in
effect for southern Florida and the Keys.

...Kentucky...

Isolated flash flooding possible across eastern Kentucky and points
eastward this morning. Individual storms will be capable of
producing 1-2 inches/hour, particularly over a part of the country
that is vulnerable to these intensities. Please refer to Mesoscale Precipitation Discussion #1045 for additional details.

Campbell/Chenard/Kleebauer


Day 2
Valid 12Z Fri Sep 05 2025 - 12Z Sat Sep 06 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR SOUTHEAST
ARIZONA AND SOUTHWEST NEW MEXICO....

...Southwest...

The exact track of the circulation from Lorena as it approaches
Sonora from the California Baja remains a bit uncertain within the
latest guidance. Some of the model guidance remains particularly
aggressive with holding the center of circulation to the
International border, just south of southeastern Arizona leading to
multiple solutions (GFS/RRFS/NAM/HAFS suite/HWRF) indicating a
swath of heavy rainfall impacting at least portions of southeast
Arizona into southwest New Mexico. ECMWF/CMC and mean ensemble
output remains not as aggressive as the previous models referenced
putting a little more emphasis on the low degrading prior to
reaching northern Sonora leading to the remnant moisture field not
advecting further north.

Assessment of the guidance compared to reality is important in
this scenario as major discrepancies early on would very well
inhibit model outputs through the course of the run. As of now, the
cluster with the greater outputs over Arizona/New Mexico are
handling the system a bit better which trends more in favor of the
wetter solutions as we move forward in time. Ensemble bias
corrected QPF was also particularly wet aiding to a little better
consensus on what could transpire across the high deserts near the
border. Ensemble totals between 1.5-3" with locally higher are
being forecast in those more substantial outputs, a range that
would cause some flash flood concerns, especially when you add in
the more effective warm rain processes being depicted when looking
at forecast soundings over parts of the aforementioned area. PWAT
anomalies closer to 3 deviations above normal would be common in
the current expected evolution, plentiful for more locally
significant impacts.

The large Marginal risk area spans from Oregon and as far east as
Colorado and New Mexico. The overall synoptic pattern favors
isolated to scattered convection over this entire area, and the
forecast PWs and instability would support locally heavy rainfall rates.

...South Florida...

The overall pattern described during the Day 1 period is not
expected to change much and locally heavy rain between 2-4" are
forecast in the period, however its location will certainly be
important with the urban centers the most favorable for at least
scattered flash flood prospects. The large scale pattern becomes
more meridional by Friday, with upper level flow becoming more
southerly over south Florida and the upper jet orientation favoring
a bit more upper level divergence. Thus could potentially see a
pattern that may favor more of a stationary or training convective
threat along the urban corridor of southeast Florida. A Marginal
Risk remains in effect for southern Florida and the Keys.

Campbell/Kleebauer/Chenard


Day 3
Valid 12Z Sat Sep 06 2025 - 12Z Sun Sep 07 2025

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FROM TEXAS TO
THE PACIFIC NORTHWEST, SOUTHERN FLORIDA AND NEW ENGLAND...

...West, Southwest and Southern Plains...

During this period a frontal boundary will stretch from the Gulf
westward into Texas. Some enhanced moisture left over from Lorena
and instability will be present over the Southern Plains, which
could allow for locally heavy rainfall to occur. A broad Marginal
is in effect for the western half of Texas into the southern High
Plains, Colorado, Southwest, Great Basin, Idaho and Oregon.

...Florida and New England...

The frontal system over Florida and northeast in the western
Atlantic will provide a focus for moisture to pool, leading to at
least scattered diurnal convection each day. Excessive rainfall
across Florida will likely focus across the southeast peninsula in
Miami-Dade County and vicinity. The Marginal Risk up north covers
most of Vermont, New Hampshire and Maine.

Campbell
$$
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FOUS30 KWBC 050808
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
408 AM EDT Fri Sep 5 2025

Day 1
Valid 12Z Fri Sep 05 2025 - 12Z Sat Sep 06 2025

...THERE'S A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
SOUTHWEST, PORTIONS OF THE TENNESSEE VALLEY, AND FOR SOUTH FLORIDA...

...Southwest...

Monsoonal moisture combined with some of the remnant moisture from
Lorena will impact much of the Southwest today. However, with
Lorena's low-level circulation now expected to dissipate offshore
and not move northeastward into northern Mexico, the share of that
moisture making it into the Southwest has been steadily decreasing.
The result is less coverage of showers and storms in favor of a
more showery weather regime. In coordination with TWC/Tucson, AZ
and EPZ/El Paso, TX forecast offices, the inherited Slight Risk for
portions of Arizona and New Mexico was removed with this update.

...Tennessee Valley...

Training thunderstorms, some of them severe, on the tail end of a
wound-up occluded front, will track northeastward along the western
side of the Appalachians this afternoon and evening. While the
storms are likely to be fast-moving, the influx of moisture
parallel to the cold front approaching from the northwest will
favor a period this afternoon where storms could redevelop and
train along the same areas in the form of multiple clusters of
storms. Thus, a new Marginal Risk was introduced covering Middle
Tennessee and into eastern Kentucky. The greatest threat of flash
flooding looks to be in the urban areas in and around Nashville.

...South Florida...

A stalled out tropical wave at the tail end of a front well off the
Eastern Seaboard will continue to plague much of the Florida
Peninsula with showers and slow-moving and erratic thunderstorms
this afternoon into this evening. While the bulk of the expected
rainfall is expected to target south Florida and the Keys, some of
that rainfall activity may sneak a bit further north into central
Florida. The greatest threat for flash flooding will be into the
highly urbanized I-95 corridor from Palm Beach through Miami this
afternoon and this evening. Given inherent uncertainty with where
the storms will set up and how they will be moving, a Marginal Risk
remains in place, though local areas where storms are the most
persistent could quite possibly have higher-level impacts.

Wegman


Day 2
Valid 12Z Sat Sep 06 2025 - 12Z Sun Sep 07 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE INTERMOUNTAIN WEST, FLORIDA, AND THE NORTHEAST...

...Intermountain West...

Monsoonal moisture will continue to steam northward across portions
of the West on Saturday. While some of that moisture can be
directly attributed to the remnants of Lorena, Lorena will have
long since ceased existing as a tropical entity by this period on
Saturday. Thus, the forcing mechanisms for heavy rain will turn to
more typical monsoonal factors, such as upsloping and an impinging
shortwave trough. For some areas, this will result in a higher
threat for heavy rain and subsequent flooding, particularly into
far southern Arizona and much of New Mexico. Nevertheless, no one
forcing will be strong enough to promote organization and more
robust heavy rains, so the Marginal Risk for the area remains in
place. Further north, a digging shortwave trough will be the
primary focus driving the heavy rain, as the storms tap into some
of that monsoonal moisture.

...Northeast...

The cold front that was moving into the Appalachians on Friday will
continue across the urban corridor of the Northeast on Saturday.
Diurnal heating and robust moisture transport up the I-95 corridor
will support training storms, which may be locally enhanced with
upslope flow from the DC Metro area northeast through Boston and
into Maine. Corfidi Vectors parallel to the frontal interface
suggest fast-moving training thunderstorms will be common. The
widespread urbanization along I-95 also supports at least a
Marginal/isolated flash flooding risk. It will be far from a rainy
day for most, with most areas staying dry. However, when storms
move through, they will likely be strong, with abundant moisture to
tap into. Thus, the inherited Marginal Risk was expanded well south
and west to include all of the I-95 corridor through the DC Metro
area. Localized urban flooding will remain the primary threat from
any repeating storms despite very dry antecedent conditions. The
front will continue eastward into Saturday night, ushering in yet
another cool and very comfortable air mass from Sunday through much
of next week. The rainfall forecast has most notably increased
across portions of New England, from NYC north. This is where the
greatest risk of flash flooding will be on Saturday.

...Florida...

The stalled out front and associated tropical wave will slowly
begin to retrograde back towards the north on Saturday, resulting
in a spreading of the potential for heavy rains well up the Florida
Peninsula. Thus, the Marginal Risk was expanded north through
central Florida with this update. High uncertainty as to
convective coverage and behavior will keep a Marginal going for the
time being, but there remains some potential a later Slight may be
needed in portions of Florida.

Wegman


Day 3
Valid 12Z Sun Sep 07 2025 - 12Z Mon Sep 08 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS AND THE FLORIDA PENINSULA...

...Southern Plains...

While some monsoonal moisture will linger in portions of the West
into Sunday, there will be far more of a Gulf component to the
moisture as predominant southeasterly flow advects deep Gulf
moisture into south Texas, which will combine with what moisture is
left from the monsoon. While the moisture will be plentiful, the
forcing will be anything but, as a strong upper level ridge builds
across the area. The result will be storms that for many areas will
be tied to the mountains, cold pools from other storms, or
localized pockets of higher instability. Thus, storm organization
across Texas on Sunday will be quite lacking. Given this, despite
the atmospheric moisture, soils across south Texas are quite dry,
which is average for this time of year. Thus, for most areas, rain
from any storms will be largely beneficial and will soak into the
ground, precluding much flooding threat. Thus, in coordination with
EWX/San Antonio, TX, CRP/Corpus Christi, TX, and SJT/San Angelo, TX
forecast offices, the inherited Slight for portions of the Hill
Country was removed with this update.

...Florida Peninsula...

It's the same old song and dance weather-wise across Florida once
again on Sunday. The front that has been stuck there will still be
there, taking advantage of plentiful Gulf/Atlantic moisture.
Uncertainty with how the storms will form and organize remains
high, so the Marginal Risk remains in place, with a northward
expansion included to account for potentially heavy rains across
central Florida from the day Saturday continuing into Sunday.

Wegman
$$
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FOUS30 KWBC 060953
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
553 AM EDT Sat Sep 6 2025

Day 1
Valid 12Z Sat Sep 06 2025 - 12Z Sun Sep 07 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PHILADELPHIA
THROUGH THE NEW YORK CITY METRO...

...Northeast...

The combination of several ingredients all at the same time in an
urban corridor has increased the potential for flash flooding. A
healthy LLJ will advect abundant Gulf/Atlantic moisture north, up
the Eastern Seaboard on Saturday. Expect PWATs to exceed 1.75
inches from Florida into New England as a result of the 25-35 kt
850 mb LLJ moving that moisture northward. Meanwhile, a strong but
rather slow-moving cold front is approaching the Northeast from the
Great Lakes. This cold front will act as a catalyst/forcing
mechanism for numerous showers and thunderstorms to develop this
afternoon in the warm, muggy air mass. Meanwhile, in the upper
levels, a 130 kt SSW to NNE oriented jet will be in place from
western Pennsylvania north to near the southern tip of Greenland.
This puts the urban corridor in the favorable right entrance region
of that jet streak, which will support lift and additional
thunderstorm development. Finally, the storms and strongest forcing
will be moving through the area at peak heating in the mid-
afternoon. This will allow the storms to be at their strongest with
the maximum amount of heating having occurred prior the convective
initiation. A subtle upper level shortwave will also move through
the jet and enter the jet streak this afternoon. This shortwave
will support additional convective development to occur behind the
initial line of storms. This additional convective development
expected is depicted in several of the CAMs model runs, most
notably the 00Z HRRR. While never a perfect prog, the HRRR's
solution if even close to correct will result in multiple inches of
rain from Philly north through NYC. Similar solutions are depicted
in the ARW2, RRFS, and NAMnest.

Expect an initial line of storms to move across northern New Jersey
and into the NYC Metro during the mid to late afternoon, between
3-6pm, with additional lines of progressively weaker convection
moving across the region well into the evening. While most areas
have been very dry of late, with the initial stages of drought
setting in, the consensus of most of this overlapping/training
convection is for it to follow I-95 from Philly up into the NYC
metro, where heavy urbanization has locally lowered FFGs. Thus,
despite empty streams and creeks, multiple rounds of heavy rain in
either continuous or rapidly repeating fashion is still likely to
cause widely scattered instances of flash flooding where the storms
are most persistent over urban areas. In coordination with
OKX/Upton, NY and PHI/Mount Holly, NJ forecast offices, a Slight
Risk upgrade was introduced with this update.

Further north into New England, the forcing is not as likely to
align as areas further south, and therefore only one or two lines
of storms are expected in this area, which has also been very dry
in recent weeks. This should limit flash flooding to isolated
instances. Further south into the DMV, once again expect a line of
storms to move through during the afternoon, but with the forcing
further north, little if any backbuilding or additional convective
development is expected behind the initial line of storms.
Nevertheless with an abundance of moisture available for the storms
to tap as they rumble across the Mid-Atlantic, as well as other
urban concerns, the Marginal Risk remains in place through much of Virginia.

...Tennessee Valley...

The same cold front moving across the Mid-Atlantic and Northeast
will also slowly push south across the Tennessee Valley today.
Being closer to the primary moisture source (the Gulf), storms in
this area will have even more moisture to feed from. However, the
front pushing south will strongly limit any potential for training
or backbuilding. Thus, for most areas, just one round of storms is
all that can be expected. Cell mergers and pre-linear convective
development could allow for isolated instances of flash flooding,
so a Marginal Risk was expanded from the Mid-Alantic down through
Tennessee and northern portions of the Southeast.

...Florida...

A stalled out front draped across the state, as well as an
abundance of deep tropical moisture in place will support yet
another round of afternoon and evening thunderstorms across much of
the Peninsula today into tonight. Since the front, while present,
will be quite diffuse, the guidance is in poor agreement as to
where any storms may organize over Florida, so a larger Marginal
Risk is all there is the confidence for, especially considering the
larger amounts of rain needed to get flash flooding in much of
Florida. The inherited Marginal Risk is largely unchanged.

...West...

Very few changes were needed out west for expected continued
monsoonal convection across much of the Southwest/Four Corners
region. The Marginal risk area was expanded a bit down the Rio
Grande in west-central Texas, but otherwise the area remains
largely the same with few changes. As is typical with the monsoon,
there will likely be feast or famine with many of the storms across
the Southwest today. Most areas will be dry or only see some light
rain, but where the storms are able to organize and concentrate,
some areas may see multiple inches of rain. Given the area's
proclivity to flash flood, the Marginal remains in place for most
of the West.

Wegman


Day 2
Valid 12Z Sun Sep 07 2025 - 12Z Mon Sep 08 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE SOUTHERN
HALVES OF TEXAS AND FLORIDA...

...Texas...

Gulf moisture in place across Texas will interact with some of the
remnant moisture from former Hurricane Lorena on Sunday. PWATs
rising to between 1.75 and 2 inches will be enough moisture to
support widely scattered convection across much of the southern
half of the state. There's considerable disagreement on the
guidance as to where the most convection will organize. Since the
overall forecast is little changed from the inherited forecast, the
Marginal Risk remains largely in lace with few changes.

...Florida...

The stalled out front that remains across Florida will extend
northeastward off the coast of the Carolinas on Sunday. Thus,
expect yet another round of afternoon and evening convection over
much of the Florida Peninsula. There remains some indication that
the convection will favor the eastern side of the state, but since
the area remains in a pattern where much of the Peninsula sees
numerous showers and thunderstorms developing each afternoon, but
with little in the way of organization to them, the inherited
Marginal remains roughly the same, depicting all of the southern
half of the state in an isolated risk for flash flooding. This is
most likely should any storms develop and sit over urban areas, or
in an area that has seen particularly heavy rain in recent days.

Wegman


Day 3
Valid 12Z Mon Sep 08 2025 - 12Z Tue Sep 09 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
FLORIDA PENINSULA AND THE GEORGIA COAST...

...Southeast...

As on previous days, much of the Florida Peninsula will remain
under the influence of a stalled out front that has been sitting
over the state for much of the past week. This will result in yet
another afternoon of numerous convection, which will take advantage
of abundant tropical moisture in the area to support additional
convective development from prior storms' cold pools. Meanwhile,
the front as a whole will very slowly drift northwestward with
time, which will spread the rain chances along the beaches from
Georgia through the Carolinas. There's high uncertainty as to
whether most of the rainfall will even make it to the coast.
Outside of Florida, the coastal areas most likely to see heavy rain
will be the Georgia coastal communities. Otherwise, as in previous
days, there will be little to support organized convective growth
across Florida, so the storms behave erratically in the guidance,
with no particularly strong signals for heavy rain anywhere in
Florida. Therefore, once again, the Marginal Risk remains in place.

Elsewhere, there are a few signals for potential heavy rain into
portions of the upper Midwest, as well as coastal Oregon. In both
areas, the signals are diffuse enough as to preclude any Marginal
Risk issuance for this update. They will continue to be watched, as
any increase in the signal for heavy rain may require a Marginal
Risk issuance.

Wegman
$$
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FOUS30 KWBC 070712
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
312 AM EDT Sun Sep 7 2025

Day 1
Valid 12Z Sun Sep 07 2025 - 12Z Mon Sep 08 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHERN TEXAS AS WELL AS FOR THE SOUTHEAST COAST AND MUCH OF FLORIDA...

...Southern Texas...

The combination of weak "ridge riding" upper level disturbances, a
strong cold front approaching from the northeast, and abundant Gulf
moisture will all poorly come together across portions of southern
Texas from now through the day today and into tonight. Storms
circulating around a well-defined upper level high over
northeastern Mexico are being driven in part due to upsloping in
the easterly flow off the Gulf. Due to the aforementioned poor
merging of these various ingredients and forcings, expect widely
scattered to scattered convection for the rest of the predawn hours
and into much of the day today. However, these storms will really
struggle to organize to result in any more than an isolated flash
flooding threat. High FFGs, about as high as they get, are
plentiful over much of southern Texas, while soil moisture levels
are about average, which works against flash flooding. Thus, any
isolated flooding in southern Texas today will require slow moving
storms hitting just the right area, likely an urban one, to cause
any impacts today.

...Southeast Coast and Much of Florida...

An area of abundant tropical moisture with embedded weak
troughs/waves will remain around the Florida Peninsula today. The
strongest trough will approach the Gulf Coast side of the state
today from the west. Interactions of this trough, any sea breezes,
and the instability difference in the afternoon between the hotter
Peninsula and the adjacent Gulf and Atlantic will be the primary
forcing mechanisms for any storms. Thus, while storm coverage will
likely once again be widely scattered to scattered. The various
forcings likely competing with each other will work to keep any
storms and clusters of storms from organizing into a more
significant flash flooding threat. Further, despite days of
scattered convection across the Florida Peninsula, soil moisture
levels across much of the state remain below normal, meaning most
of the rain that falls from the afternoon and evening storms will
remain beneficial for most. Thus, the Marginal flash flooding
threat is primarily focused on urban areas today, as any storms
will have plenty of moisture to draw from to locally produce multiple-inch-per-hour rainfall rates.

...New England...

The inherited Marginal Risk across the area was dropped with this
update. All of the rainfall across New England this morning is
stratiform, struggling to produce rates even to a half inch per
hour. This is likely to continue today as the cold front causing
the rain continues to press east towards the coast. While a few
areas of embedded convection from mid-level instability can't be
ruled out, fast motion will also cut into the rainfall amount any
one area picks up today.

Wegman


Day 2
Valid 12Z Mon Sep 08 2025 - 12Z Tue Sep 09 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE CENTRAL PLAINS AS WELL AS FOR THE FLORIDA PENINSULA...

...Central Plains...

An area of convection across the central Plains early Monday
morning will be ongoing at the start of the period. The storms will
develop along a warm frontal interface, where a seasonably cold and
dry air mass will be in place across much of the eastern half of
the country, meanwhile warmth and moisture will be moving north on
an LLJ up the Plains to the west. This will result in a somewhat
unusual scenario where the eastward moving storms will be moving
into a very hostile environment. This will greatly impede the
storms ability to make eastward progress. Thus, the greatest flash
flooding threat, albeit isolated, will be in the area where the
storms form. This is most likely Monday morning across central
Kansas. By mid to late morning, typical diurnal heating will
disrupt the warm frontal interface, with the collapse of the
forcing resulting in the typical weakening of the convective
complex across Kansas. Isolated to widely scattered convection will
continue in fits and spurts over eastern Kansas and adjacent areas
of the neighboring states, but the storms are unlikely to regain as
much organization as they'll have in the early morning hours
Monday. Renewed convection may form further east towards the Kansas
City Metro Monday night, but once again are unlikely to be quite as
organized and have as much coverage as Monday morning's convection
further west.

...Florida Peninsula...

Monday will be a repeat scenario of many afternoons of the past
week or more across Florida. A stationary plume of tropical
moisture will remain firmly entrenched across the state. A nearly
stationary low over the western Gulf will draw additional moisture
and storms towards the west coast, while stationary fronts,
boundaries, and old cold pools will locally provide their own
forcing Monday afternoon. Thus, the result will be the
same...multiple clusters of storms popping up at random across much
of the Florida Peninsula, but just as often as not competing with
each other. Once again, any isolated flash flooding threat will be
where cell mergers or slow moving storms happen to stall out over
urban or other flood prone areas.

Wegman


Day 3
Valid 12Z Tue Sep 09 2025 - 12Z Wed Sep 10 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
SOUTHEASTERN COAST AND THE FLORIDA PENINSULA AS WELL AS FOR
PORTIONS OF NORTHERN IDAHO AND WESTERN MONTANA...

...Southeast...

A trough that has been parked across the Florida Peninsula for well
over a week and associated boundary that has been off the coast of
the Carolinas for the past several days will begin to move
northwest back towards the coast as a warm front on Tuesday. A
mesolow may form along the front which may also help move the heavy
rain associated with the boundary northwestward towards the coast
of the Carolinas. The trough, while it has been in place for an
extended period of time, still will demarcate a strong boundary
between a cool, Fall-like air mass over much of the East Coast, and
a typical summery airmass characterized by hot and very humid
conditions. Thus, the trough will still be plenty able to provide
the forcing for strong thunderstorms capable of heavy rain. As the
heavy rain approaches the coast Tuesday, any flash flooding for
coastal communities will result from that heavy rain,
urbanization, and a coincident high tide. Uncertainty with where
exactly that axis of heaviest rain will set up will preclude any
possible upgrades to the ERO at this time, but too much more of a
westward shift of the heaviest rain into the coast will support
possible upgrades in future updates.

Meanwhile over Florida, the primary forcings will be a slow and
erratic moving low over the western Gulf, and the front/trough
centered off the coast, but moving towards the coast. There is
greater potential for more widespread rains across the Florida
Peninsula on Tuesday due to these two forcings moving in closer
proximity to each other. Regardless, any potential Slight Risk
upgrades will be highly dependent on the rainfall footprint of
prior days' rains.

...Pacific Northwest...

A large cutoff low parked over Washington State and Oregon will
pinwheel several pieces of shortwave energy northward along its
eastern periphery across Idaho and Montana on Tuesday. Abundant
forcing and upslope support will use what moisture is available to
result in scattered convection across the region Tuesday afternoon
during peak heating. Since the cutoff low will be barely moving,
this will allow for an extended period where the region will be in
the most favorable region for widespread lift. Thus, while the
heaviest rainfall rates and most widespread convective converage
will be in the afternoon and evening during peak heating, showers
and storms will continue both before and after this time period,
contributing to an isolated flash flooding threat. Should forecast
moisture availability increase during this time with future
updates, there is some potential a targeted Slight Risk area may be needed.

Wegman
$$
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FOUS30 KWBC 080858
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
458 AM EDT Mon Sep 8 2025

Day 1
Valid 12Z Mon Sep 08 2025 - 12Z Tue Sep 09 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTION OF
OREGON, NORTHERN CALIFORNIA, THE SOUTHERN AND CENTRAL PLAINS, THE
UPPER MISSISSIPPI RIVER VALLEY, AND FLORIDA PENINSULA...

...Texas Panhandle into the Central Plains...
An ongoing convective complex is expected to produce areas of
locally heavy rainfall across central/eastern Kansas toward the
beginning of the forecast period (early Monday morning).
Convergence on the nose of strong low-level flow amid modestly
steep mid-level lapse rates aloft are likely to sustain the storms
for a few hours (between 12-18Z Monday) before veering and
weakening low-level flow causes weakening. Local
backbuilding/training could result in rates exceeding 1 inch/hr
locally, which may result in a few issues with excessive runoff.

Isolated thunderstorm activity is expected from southwestern Kansas
through the Texas Panhandle during the afternoon and evening hours.
The Marginal Risk is being maintained for consistence with prior
forecasts, although newest models depict modest convective
coverage. Nevertheless, supercellular wind profiles and steep lapse
rates aloft may result in intense convection and local rain rates
exceeding FFG for a few hours during the afternoon and early
evening. This Marginal is conditional on sufficient convective
coverage for localized prolonging of heavier rainfall.

Lastly, models depict a resurgence of elevated convection on the
nose of strong low-level flow. The best convergence (and resultant
convective coverage) should extend from southeastern Nebraska south-southeastward along the Kansas/Missouri border region.
Localized backbuilding and training could result in spots of 2-4
inch rainfall totals, and flash flooding is possible on an isolated
basis. Soil moistures are relatively dry though, further suggesting
only an isolated flash flood threat.

...Oregon, northern California...
A substantial mid-level system will approach the region from the
northeastern Pacific during the afternoon and evening.
Ascent/cooling aloft will be well aligned with peak heating,
resulting in sufficient instability for widespread showers and
occasional thunderstorms. Recent CAMs suggest an area of focus for
convection across higher terrain of southwestern Oregon (near the
Medford area) and into terrain-favored areas of northern
California. Appreciable mid-level lapse rates and PW values
approaching 1 inch suggest potential for several areas of wetting
convection, and areas of flash flooding are possible especially
near burn scars and low-lying, flood prone areas. Deeper convection
may also extend toward northern Oregon along the Columbia River
Basin, with isolated flash flood potential expected.

...Upper Mississippi Valley...
Low-level warm advection across a warm frontal zone from the
Dakotas into Iowa should result in areas of showers and
thunderstorms by 00Z. The orientation of this convection favors
some training/backbuilding that could enhance rain rates locally.
2-3 inch totals are expected, with locally higher amounts possible
particularly across northeastern Minnesota.

...Florida...
A nearly stationary front will remain across northern Florida.
Abundant moisture (2+ inch PW values) should reside south of this
front. A weak low should also reside just west of the state over
Gulf of America waters. Convection is expected to develop over much
of the Peninsula in tandem with daytime heating and
destabilization. Cells should remain relatively slow-moving, with
areas of 2+ inch/hr rain rates (and 3 inch totals) expected
throughout the forecast period. Isolated flash flooding is possible
especially where these heavier rates can materialize over
urbanized/sensitive areas.

Cook


Day 2
Valid 12Z Tue Sep 09 2025 - 12Z Wed Sep 10 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
FLORIDA PENINSULA...

Few changes were made from the inherited Marginal Risk area
inherited from yesterday's Day 3 ERO. The quasi-stationary surface
boundary over north Florida early Tuesday will nudge slowly into
central FL by Wednesday morning as southern periphery of the mid-
upper level trough remains parked across the central Gulf Coast
region. Continued large-scale forcing downstream of the upper
trough -- weak upper level difluence and subtle shortwave
energy/periodic DPVA -- will again favor more widespread/organized
convection during the peak heating hours from late morning into
early evening on Tuesday. Low-level convergence over the eastern
peninsula will likely get a boost from the sea- breeze component,
as the southwesterly low-level flow weakens and backs more
southerly near the east coast. As a result, could see more
widespread convective clusters and heavier rain farther east toward
the I-95 corridor, as supported by the higher HREF and RRFS
probabilities of 2-3 inch/hr rainfall rates across this area after
17Z Tuesday. Thermodynamic parameters will be more than supportive
for highly efficient warm rain processes, with mixed-layer CAPEs at
least 1000-2000 J/Kg, TPWs of 2.2-2.3", and wet bulb zero levels
above 14KFT (optimal warm layer depth). Moreover, 0-6km bulk shear
values around 20-25 kts should allow for more convective
organization, though the degree of downwind propagation
(southwesterly Corfidi vectors around 10-15kts) should inhibit the
potential for cell training.

As a result, any excessive short-term runoff on Tuesday will be
localized and likely tied to urban and/or poor drainage areas.

Hurley


Day 3
Valid 12Z Wed Sep 10 2025 - 12Z Thu Sep 11 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF
THE NORTHERN GREAT BASIN AND MUCH OF THE FLORIDA PENINSULA...

...Northern Great Basin east of the Cascades and Shasta Siskiyous
to central and northern Idaho...

Deep/closed upper low centered near the OR/CA/NV tri-state area
will average around 2 standard deviations below normal for early
September. Plenty of deep-layer Qs forcing (upper
difluence/divergence and periodic DPVA) will combine with above-
normal moisture (TPWs near 1.0" or 2-2.5 standard deviations above
normal) and sufficient diurnal instability (MUCAPEs 500-1000 J/Kg) to
produce locally excessive rainfall across portions of the northern
Great Basin Wednesday. The 00Z global guidance all show a modest
rainfall footprint, with the ensemble blends showing areal-average
totals between 0.50-1.00" within much of the outlook area.
However, largely tied to the degree of deep-layer instability and
available moisture, localized heavier totals were noted (2-4+
inches per the RRFS, GFS, and CMC), albeit with considerable areal
spread. The GEM in particular was most robust, noting a swath of
3-5+ inches across central OR east of Bend. For now, given the
spread in the guidance QPFs, will keep the ERO Risk at Marginal,
though this setup synoptically certainly would have the potential
for a more enhanced (i.e. Slight) risk as the event draws near.

...Florida Peninsula...

Similar setup to Tuesday, though the guidance shows a bit more
robust shortwave activity SW-NE across the Peninsula along and
south of the surface front which should remain quasi-stationary
across central FL on Wednesday. As a result, the multi-model
blend is higher with the QPF in terms of areal-average (ensemble
mean) on Wed compared to Tue, particularly over the central and
eastern portion of the peninsula where some backing in the low-
level flow (from the Atlantic sea breeze) will likely enhance the
low-level convergence due. Once again though given the downwind
propagation (S-SW Corfidi Vectors ~10+ kts), anticipate progressive
cell motions while not expecting much in the way of persistence or
training of the convection. Therefore the excessive rainfall risk
remains Marginal given the more isolated/localized risk for flash flooding.

Hurley
$$
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FOUS30 KWBC 100804
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
404 AM EDT Wed Sep 10 2025

Day 1
Valid 12Z Wed Sep 10 2025 - 12Z Thu Sep 11 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE URBAN I-95 CORRIDOR OF SOUTH FLORIDA...

...Florida...

A stationary front draped across north Florida will remain in place
as abundant tropical moisture, characterized by PWATs over 2
inches, streams across the state and along that front. Within that
moisture plume over much of the southern half of Florida, numerous
showers and thunderstorms are likely to form with peak heating
this afternoon. As on previous days, despite the front to the
north, over most of the peninsula, there are likely to be many
different sources of forcing for the storms. Without a coherent
source allowing the storms to organize, it's likely the storms will
remain individual or form into small clusters. While there will be
plenty of moisture for the storms to be capable of heavy rainfall
with any stronger core, without organization it appears unlikely
that for most of the peninsula, there will be more than isolated
instances of flash flooding.

Across the urban I-95 corridor, however, multiple prior days'
rainfall has thoroughly saturated any soils. Thus, when heavy rain
occurs with the afternoon and evening convection, there is more
likely to be widely scattered instances of flash flooding. Thus,
the Slight Risk area inherited remains unchanged with this update.

...Pacific Northwest...

A large upper level low and associated trough covering much of the
West Coast will gradually drift east/inland across the
Intermountain West today. Shortwave energy rotating around the low,
interacting with the instability caused by the cold air aloft and
unusually high amounts of atmospheric moisture (anomalies to 2.5
sigma above normal) will allow several clusters of showers and a
few storms capable of heavy rainfall to form. Upslope enhancement
may also locally increase rainfall rates as any clusters of showers
and storms move through. While some minor tweaks were made to the
Marginal, especially in northern California, the forecast remains
largely the same.

Wegman


Day 2
Valid 12Z Thu Sep 11 2025 - 12Z Fri Sep 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTH FLORIDA...

...Florida...

The stationary front plaguing Florida for well over a week will
begin to move as a cold front on Thursday, as a reinforcing shot of
cooler and drier air pushes south across the Southeast. As the
front pushes south down the Peninsula, the front should act as a
source of forcing for the storms, allowing for greater organization
and greater areal rainfall across South Florida as compared with
previous days when the forcing was far less defined. Add in the
saturated soils across south Florida, and the area where flooding
could be more frequent than isolated instances expands north up the
I-95 corridor towards the advancing front. Thus, the Slight was
expanded north accordingly.

...Pacific Northwest into the Northern Plains...

A plume of anomalously high moisture in place from the Pacific
Northwest to the Northern Plains will support scattered showers and thunderstorms forming once again along a corridor from eastern
Oregon through much of northern Montana. A separate cluster of
storms may sneak south across the Canadian border and into far
northeastern North Dakota and northwestern Minnesota as well. Due
to the potential for heavy rain in all of these areas, a Marginal
Risk is in place and has been expanded eastward to cover the areas
most likely to see isolated instances of flash flooding from heavy
rain from these features.

...Western Colorado and Far Northwestern New Mexico...

Southerly flow on the western edge of a low-level jet across the
Plains will transport Gulf moisture into the region on Thursday.
Meanwhile the large trough out west will become positively tilted
with time. This will allow an 80 kt jet southwesterly jet streak to
form, which will increase the divergence aloft across this area.
Expect upslope into the high peaks of southwestern Colorado to
locally enhance rainfall totals, thereby increasing the flash
flooding risk. Soil moisture measurements from NASA Sport show much
of this area to be below average/drier than normal. Thus, expect
much of the rainfall Thursday in this region to work to saturate
the soils in anticipation of Day 3/Friday's bigger rainfall event.

Wegman


Day 3
Valid 12Z Fri Sep 12 2025 - 12Z Sat Sep 13 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTH FLORIDA AS WELL AS FOR PORTIONS OF NORTHWESTERN NEW MEXICO
INTO SOUTHWESTERN COLORADO...

...Northwestern New Mexico into Southwestern Colorado...

A positively tilted longwave trough centered over much of the
Intermountain West on Friday will become more neutrally tilted on
Friday as a strong shortwave trough causes the southern half of the
trough to begin to race eastward. The result will be even more
enhanced upper level divergence out ahead of the trough over New
Mexico and Colorado. Atmospheric moisture will be largely unchanged
in this area from Thursday. With peak heating Friday afternoon,
numerous showers and thunderstorms will form over nearly all of the
High Plains. However, coverage and intensity will be much higher
in the Slight Risk area in Colorado and New Mexico. The area is
likely to be the same one hard hit from the Day 2/Thursday period,
so expect soil moisture amounts to be higher and FFGs to be lower
over much of the area by Friday's event. Given all of these
ingredients in place and in coordination with GJT/Grand Junction,
CO forecast office, a Slight Risk upgrade was introduced with this update.

...South Florida...

The cold front across central Florida at the start of the day
Friday will make slower, but still incremental progress in its
southward movement down the peninsula. The plume of tropical
moisture across south Florida ahead of the front will also still be
in place. Thus, as is similar to Thursday over the middle of the
state, the axis of heaviest moisture will simply shift southward to
far south Florida on Friday. The inherited Slight Risk area was
expanded west over much of the Everglades and portions of southwest
Florida with this update, to follow more closely to where the axis
of heaviest rainfall is likely to set up. Given the focus will
shift into the more vulnerable and flood prone urban areas of south
Florida, its entirely possible that a higher end Slight risk will
need to be issued for the Ft. Lauderdale to Miami corridor with
future updates.

...Northern High Plains...

Similar to Day 2/Thursday, anomalous moisture will remain in place
across much of Montana and portions of adjacent states again on
Friday. The upper level low and trough will move overhead or just
south of the region on Friday. As the cold air aloft peaks in depth
on Friday, numerous showers and thunderstorms are likely to
redevelop again on Friday afternoon with peak heating and maximum
instability. The axis of heaviest rain from central Idaho through
northwestern Montana will also be largely unchanged and unmoving
from Thursday, meaning these areas will likely have a second day of
showers and storms capable of heavy rain and flooding again on
Friday. Thus, here too a Slight Risk upgrade may be needed with
future updates. This will largely be determined by how much rain
falls on Thursday in this area, which will prime the soils for
Friday's round of rain.

Wegman
$$
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FOUS30 KWBC 110811
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
411 AM EDT Thu Sep 11 2025

Day 1
Valid 12Z Thu Sep 11 2025 - 12Z Fri Sep 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTH FLORIDA...

...South Florida...

A quasi stationary front over central Florida will make incremental
southward progress down the Peninsula today. Ahead of this source
of forcing, atmospheric moisture levels across south Florida remain
very high, with PWATs above 2 inches. With afternoon heating,
MUCAPE levels will once again rise to between 2,000 and 3,000 J/kg.
This will support numerous showers and thunderstorms developing
over the southern half of the state, and generally moving southward
through the afternoon. However, as is typical of Florida afternoon
convection, while the overall storm motion may be southward,
localized forcing such as cold pools and sea breezes may make
individual cell motion far more erratic. Given that soils across
much of the Florida Peninsula are fully saturated after weeks of
afternoon convection each and every day, this will still pose a
widely scattered flash flooding risk, particularly along the urban
I-95 corridor. However, given the saturated soils, the threat
extends into much of interior south Florida as well. The inherited
risk areas were trimmed from the north to eliminate most areas that
are already behind the front, and therefore much drier.

...Northwest...

An area of well above average moisture on the northwestern side of
a nearly stationary longwave trough/cutoff low over the
Intermountain West will act as a focus for additional shower and
thunderstorm activity in the typically dry areas from eastern
Oregon northeast through much of Montana. While the longwave trough
will be very slow-moving, the embedded shortwaves and vort maxes
circulating around it will be faster moving, providing additional
forcing and areas of divergence for any shower and thunderstorm
development. Local mountains and ranges will also work to cause
some thunderstorm development. Thus, due to there being several
forcing mechanisms with little to note as to which will be
dominant, expect multiple clusters of storms to develop this
afternoon with peak heating. With plenty of atmospheric moisture
available for those storms, many may be capable of heavy rainfall
which could quickly cause flash flooding, especially in any urban
areas, slot canyons, and narrow river valleys.

...Western Colorado into Northwestern New Mexico...

On the eastern side of the deep longwave positively tilted trough
in the west, increased divergence and lift ahead of that trough,
supported by southerly flow of moderate amounts of Gulf moisture
will support numerous showers and a few storms forming across the
Marginal Risk area today through tonight. The key to the flooding
potential in this area will be the long duration of mostly light
rain but that will be training in this Marginal Risk area from this
afternoon through much of tonight. The Marginal Risk area remains
largely unchanged from inherited.

Wegman


Day 2
Valid 12Z Fri Sep 12 2025 - 12Z Sat Sep 13 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTH FLORIDA AS WELL AS FOR PORTIONS OF SOUTHWESTERN COLORADO INTO
CENTRAL NEW MEXICO...

...South Florida...

The front across South Florida on Friday will make additional
progress southbound down the Peninsula. The portion moving down the
west coast of the peninsula will make better progress southward
compared to the portion of the front along the East Coast. This
should support the front becoming increasingly aligned southwest to
northeast. Since the front will be moving a bit more on Friday,
there should be a bit better coverage of storms across south
Florida, where the Slight Risk area inherited remains largely
unchanged. As the front pushes south, it will shove the bulk of the
tropical moisture into the Florida Straits and into the Bahamas.
This should work to limit storm coverage on future days, as a much
drier and cooler air mass continues to envelop the rest of the state.

...New Mexico and Colorado...

The positively tilted upper level trough from Thursday will begin
to pivot to become neutrally tilted on Friday. This means the
southern end of the trough will get a boost to advance eastward,
while the northern end will largely stay in place. The result will
be a more south to north oriented axis of heavy rainfall,
stretching from the southern end of New Mexico north across much of
western Colorado. Moisture from the Pacific will also be drawn
northward along the New Mexico/Arizona border. This should expand
the rainfall footprint for Friday across much of the southern
portion of New Mexico and southeastern Arizona. Expect Friday to
the wettest day this week for New Mexico and Colorado.

CAMs guidance suggests the plume of moisture stretching NNE from
southeast Arizona through north-central New Mexico and into
Colorado will be the focus for additional convection capable of
producing flash flooding. With better southward extent, the storms
will be able to tap into some deeper moisture and instability from
the Pacific on Friday. This will make thunderstorm coverage Friday
greater than in previous days. Since the whole plume will also be
lifting north and east, expect a much larger area of rain to impact
the area Friday. Embedded thunderstorms among the mostly lighter
shower activity will be the foci for any potential flash flooding.
This will be particularly true in any areas where multiple rounds
of storms producing heavy rain occur.

...Northwest...

Shortwaves and vorticity maxes rounding the periphery of the
longwave trough will be the foci causing additional convection from
northern Idaho east across much of Montana. The expected rainfall
forecast has decreased the overall rainfall in this area. However,
mountain forcing may offset this in some areas.

Wegman


Day 3
Valid 12Z Sat Sep 13 2025 - 12Z Sun Sep 14 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM EASTERN NEW
MEXICO THROUGH SOUTHWESTERN KANSAS, AS WELL AS FOR A PORTION OF THE
URBAN CORRIDOR OF SOUTH FLORIDA...

...New Mexico through Kansas...

As the upper level trough over the Intermountain West becomes more
negatively tilted, a portion of the low level jet out ahead it will
draw deeper Gulf moisture north into the Panhandles and eastern New
Mexico and into southwestern Kansas. This will support a line of
storms that will develop over central New Mexico and then press
eastward into the Slight Risk area. Once over eastern New Mexico
and the Panhandles, the eastward progress of the storms will
diminish greatly, resulting in much slower-moving but still
organized storms. This will be the basis for training, resulting in
widely scattered instances of flash flooding where the storms are
the most persistent.

...South Florida...

The front over South Florida will finally push east and clear all
of the deepest tropical moisture well out into the Atlantic and
Bahamas by Sunday morning. Thus, expect Saturday to be a transition
day in the area...where there will still be storms, particularly
along the urban I-95 corridor from Miami through Palm Beach, but
there will be less coverage over Florida as the moisture is pushed
eastward out into the Atlantic. The newly issued Slight is a low-
confidence one, as once the front clears the state, that should end
the flooding threat. However, given the many days of daily
afternoon convection in the I-95 corridor, soils are sensitive
enough that even the reduced time and coverage of storms could
still cause widely scattered instances of flash flooding.

...Northern Plains...

Across the Northern Plains, ahead of the neutrally tilted trough
that is becoming negatively tilted, the northern extent of the low
level jet ahead of the trough will draw deeper Gulf moisture
westward across the Dakotas. This should support persistent
convection. However, this area of the Dakotas is fairly difficult
to flood, so despite the higher probability for training and heavy
rain, the area remains in a higher-end Marginal for now. A Slight
Risk upgrade may be needed for portions of the area as guidance
begins to resolve this part of the event across the northern Plains.

Wegman
$$
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FOUS30 KWBC 120805
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
405 AM EDT Fri Sep 12 2025

Day 1
Valid 12Z Fri Sep 12 2025 - 12Z Sat Sep 13 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTH FLORIDA, SOUTHWESTERN COLORADO THROUGH CENTRAL NEW MEXICO,
AND THE NORTHERN PLAINS...

...South Florida...
Stationary front persists over far South Florida today with the
positive moisture anomaly focused over the Miami metro with the
eastern coast likely to get more slow moving heavy thunderstorms
in the light mean layer flow. The Slight Risk is shrunk to be
closer to the Miami-Palm Beach metro area with the Marginal Risk
still extending up the east coast nearly to Jacksonville.

...New Mexico and Colorado...
The positively tilted upper level trough from an upper low over
northern NV will pivot to neutral tilt this afternoon. Therefore,
expect a more south to north oriented axis of heavy rainfall,
stretching from south-central New Mexico to across much of western
Colorado. Moisture from the Pacific will also be drawn northward
into eastern Arizona and western New Mexico with PW anomalies of
+1.5 to 2 sigma, resulting in a rather large QPF footprint.
Diurnal convection is the main focus at play today, though
guidance continues to suggest repeating rains over southeast AZ and
southern NM into the overnight. The Slight Risk is maintained over
southwest CO and central NM.

...Northern Rockies onto the Northern Plains...
The upper low center shifts north to MT by late tonight. Notable
activity ahead of the low/trough looks to focus over the western
Dakotas into eastern MT per 00Z CAM consensus where a Slight Risk
has been raised. PW anomalies of 1 to 2 sigma remain over northern
ID/western MT where the Marginal Risk is maintained.

...Upper Midwest...
Ongoing activity over eastern ND and northern MN should shift
southeast by 12Z and track to northern WI. Then diurnally driven
convection looks to cross a similar path. Given the advance of
moisture over the upper ridge axis extending over eastern IA, it
was worth adding a Marginal Risk to northern MN/WI and the western
U.P. of MI.


Jackson


Day 2
Valid 12Z Sat Sep 13 2025 - 12Z Sun Sep 14 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM WESTERN KANSAS
TO FAR WESTERN TEXAS, THE MIAMI METRO, AND WESTERN NORTH DAKOTA...

...Central High Plains through Southern Rockies...
The upper level trough over the Intermountain West becomes
negatively tilted on Saturday with the monsoonal moisture axis over
NM during the day shifting to the southern High Plains overnight.
The position of this trough will enhance the low level jet on the
High Plains Saturday night and draw deeper Gulf moisture north
over the Panhandles and eastern New Mexico and through western
Kansas. This will encourage diurnally developing lines of storms
from New Mexico terrain to press eastward onto the High Plains.
Given the +2 sigma PW anomalies and overall slow storm motion, the
Slight Risk area was expanded a bit over western KS and down into
far western Texas.

...South Florida...
The front will push south from Florida during the day Saturday with
anomalous moisture lingering in the morning over the Miami metro
where A Slight Risk persists. The Slight Risk still looks generous
given the decreasing moisture profile through the day, but is
maintained for now.

...Northern Plains...
The upper low center over central MT will allow the focus for
heavy convection to shift north a bit from Friday with both morning
and diurnal max activity looking to focus on western ND. Given good
overlap in heavier precip among available CAMs and the EC-AIFS, a
Slight Risk is raised over western ND. Pivoting of the low without
much lateral movement is expected, prolonged heavy rainfall is
possible with.

Jackson


Day 3
Valid 12Z Sun Sep 14 2025 - 12Z Mon Sep 15 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN THE DAKOTAS...

...Central and Northern Plains...
Negatively-tilted trough axis lifting up the central Plains Sunday
should provide a narrow focus to convective development over the
western or central Dakotas. This activity will be heavy given PW
anomalies of +3 sigma persist over this area. Further development
is expected from central KS up through the Dakotas where a generous
Marginal Risk remains in effect.

Jackson
$$
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FOUS30 KWBC 130849
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
449 AM EDT Sat Sep 13 2025

Day 1
Valid 12Z Sat Sep 13 2025 - 12Z Sun Sep 14 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR EASTERN NEW
MEXICO INTO FAR WEST TEXAS AS WELL AS FOR WESTERN NORTH DAKOTA...

...Central High Plains through Southern Rockies/West TX...

Upper trough over the Great Basin this morning will continue
slowly eastward and take on a negative tilt, with a continued
influx of moisture (PW anomalies +2 sigma) into the Southern
Rockies and points northward. As the trough axis crosses the Four
Corners region around 00Z tonight, LLJ increase will support
convection over eastern NM late afternoon that will push into West
Texas in the evening. Storms may have enough forward speed to limit
flash flooding potential, but 00Z CAMs continue to show potential
for 1-4" amounts. Focused the Slight Risk outline further from the
previous shifts to the best ensemble agreement.

...Northern Plains...

Southerly flow through the column will maintain a surge of
moisture (PW anomalies +3 sigma / 1.50") into the Northern Plains
as weaker shortwaves race northward ahead of the main upper low
over MT. Recent CAM guidance still shows some east-west
displacement of heaver north-to-south QPF maxima, owing to small
differences in shortwave/sfc boundary interactions and any morning
convection. Maintained the Slight Risk outline over western ND but
the eventual QPE footprint will likely be much narrower.

...Northeastern Illinois and surrounding areas...

Shortwave diving southeastward out of Wisconsin this morning at
the nose of a jet streak will help organize a small area of at
least modest rainfall around the Chicagoland area that continues
SSE-ward this afternoon. Some 00Z CAM guidance remains rather
bullish with 2-3" amounts which may be enough to cause some urban
runoff issues.

...South Florida...

Frontal boundary will remain just to the southeast of Florida, but
precipitable water values will start the day around 2 inches.
Drier air will slowly work southeastward through the entirety of
the Peninsula by the end of the day, and have targeted the Marginal
Risk outline to around the urban areas between Palm Beach and Miami.

Fracasso


Day 2
Valid 12Z Sun Sep 14 2025 - 12Z Mon Sep 15 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN THE WESTERN DAKOTAS...

...Central and Northern Plains...

Upper trough exiting the Rockies will split off its southern
portion into an upper low over western Nebraska midday Sunday, with
southerly flow continuing across the Northern Plains (and ample
moisture -- PW anomalies still +2 to +3 sigma). This mid-level low
will lift northward and act as a focus for convergence toward the
nose of the sfc- based instability gradient just to the east.
Storms may repeat over the same area as D1, with the potential for
another 1-2"+ of rain. Maintained the Slight Risk outline here with
a broader Marginal Risk extending to the south where the guidance
shows potential for 2-4" of rainfall, but over areas with higher
FFG values (esp. the Sand Hills).

Fracasso


Day 3
Valid 12Z Mon Sep 15 2025 - 12Z Tue Sep 16 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Fracasso
$$
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FOUS30 KWBC 140824
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
424 AM EDT Sun Sep 14 2025

Day 1
Valid 12Z Sun Sep 14 2025 - 12Z Mon Sep 15 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN THE WESTERN DAKOTAS...

...Northern Plains...

Upper trough exiting the Rockies has split off its southern
portion into an upper low that will move onto the High Plains later
this morning. Southerly flow will continue across the Northern
Plains along with ample moisture -- PW anomalies +2 to +3 sigma --
as a surface low over SD moves northward later this afternoon.
Convergent flow toward the nose of the sfc-based instability
gradient just to the east is expected to promote some south-to-
north convection that may overlap areas that saw a few inches of
rain on Saturday. Maintained the Slight Risk outline here with a
Marginal Risk buffer extending to the south to the edge of the Sand
Hills.

...Central and Southern Plains...

Split the longer Marginal Risk area from the previous forecast
into its own entity and extended it even farther southward to the
Mexican border to account for another tick up in expected
convection from KS southward to TX. Storms should fire along and
ahead of a low-level confluence axis and within a stripe of deeper
moisture. Some of these areas in W TX saw a couple/few inches of
rain on Saturday and FFG values are lower. Some models do indicate
the potential for slow-moving or backbuilding cells, resulting in
locally heavy amounts and perhaps isolated flash flooding concerns.

Fracasso


Day 2
Valid 12Z Mon Sep 15 2025 - 12Z Tue Sep 16 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Fracasso


Day 3
Valid 12Z Tue Sep 16 2025 - 12Z Wed Sep 17 2025

...THERE ARE MARGINAL RISKS OF EXCESSIVE RAINFALL IN SOUTHERN NEW
MEXICO, THE CENTRAL PLAINS, AND COASTAL VIRGINIA...

...Southern New Mexico...

Moisture will start to nudge upward over southern NM (though much
more well west of there) with some afternoon instability and
expected isolated convection, mainly over the mountains close to
the Mexican border. Low-end Marginal Risk is outlined here though
activity should be rather isolated.

...Central Plains...

Positively-tilted trough over the Northern Rockies will move
eastward to the High Plains Tuesday afternoon. Broad westerly mid-
level flow amid increasing moisture will help fire off some storms
over at least NE near the better forcing but also southward into
KS. A Marginal Risk is outlined here for an isolated flash flood
threat.

...Coastal Virginia...

Over the past couple of days, the models have trended toward
bringing in an area of low pressure near the Outer Banks Tuesday
morning or so. Rain should spread inland on Monday with additional
and perhaps heavier rain on Wednesday. This area has been rather
dry recently and rain rates may not be all that high, but some convection-driven rain is possible depending on the flavor of this
area of low pressure. A Marginal Risk is depicted for
southeastern/coastal Virginia and far northeastern North Carolina
but with a lot of uncertainty in the rainfall
pattern/rates/duration.

Fracasso
$$
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FOUS30 KWBC 150743
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
343 AM EDT Mon Sep 15 2025

Day 1
Valid 12Z Mon Sep 15 2025 - 12Z Tue Sep 16 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
EASTERN NORTH CAROLINA AND SOUTHEASTERN VIRGINIA...

Current WV satellite indicates a maturing mid-level trough situated
just off the SC/GA coast with a surface low analyzed 150 miles
east of KILM, meandering around as the upper pattern evolves.
Expectation is the surface low to be pulled northwest over the
course of the D1 with a closer proximity to the NC coast by later
this afternoon and evening with a strong east to northeast flow
anticipated over the northern flank of the SLP. Current NAEFS
ensemble output is forecasting a stout +2/+3 deviation u-vector
wind component with origins straight off the Atlantic, a signal
coincident with a robust low-level moisture advection regime into
the northern and western flank of the low pressure center. PWATs
are anticipated to climb closer to +1.5 deviations above climo,
good enough for outputs within the 1.5-2" mark across much of
eastern NC into the VA Tidewater. The persistence in the low-level
flow and modest ascent located within the maturing deformation axis
will lead to a long period of heavy rainfall situated across the
aforementioned areas above, allowing totals to reach between 2-4"
over areas along and east of I-95 and north of US70 in NC, and
between 1-3" across the VA Tidewater.

00z HREF is pretty robust in the depiction for the above totals
forecast with some embedded convective elements likely to spur
rates between 1-2"/hr at times, mainly across northeast NC where
strongest 850-700mb FGEN signals align early this evening into the
overnight hours. HREF neighborhood and EAS probs for >2" are pretty
high for the region with the neighborhood >3" signal settling
between 50-90% for the zone referenced above in NC. Antecedent
drier soils leading in will help curb some of the flash flooding
concerns initially, but the long-standing heavy rain threat, and
embedded convective potential the second half of the forecast could
lead to isolated/scattered bouts of flash flooding as the event
continues. The previous MRGL risk was expanded to align with the
trends in the >3" neighborhood prob signal in the HREF, and to
account for the latest ECMWF EFI signal extended a bit further west
than where we had the previous MRGL risk located.

Kleebauer


Day 2
Valid 12Z Tue Sep 16 2025 - 12Z Wed Sep 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHWEST, THE CENTRAL HIGH PLAINS, AND VIRGINIA/NORTH CAROLINA...

...Southwest...

Scattered convective pattern will initiate on Tuesday afternoon and
early evening before fading with the loss of diurnal heating.
Current progs are for convection to be tied closer to the terrain
across southeast AZ into southern NM with isolated signatures of

1"/hr plausible in the stronger cell cores. These areas generally

prone to runoff due to terrain complexities, as well as remnant
burn scars present in some locations. Maintained continuity from
inherited MRGL risk with some minor adjustments to remove El Paso proper.

...Central High Plains...

Strong shortwave trough ejection out of the interior Northwest will
lead to convective development and regional enhancement across the
Central High Plains. Greatest ascent is aligned with the diffluent
region of the mid-level shortwave with left-exit region dynamics
likely to maintain a prevalent heavy rain signature across the
western third of NE down into neighboring northeast CO and
northwest KS. Heaviest rain could remain just outside of the risk
area according to some guidance leading to low probability of flash
flooding due to the occurrence within the western Sand Hills.
There's still a good agreement on localized maxima within the hi-
res ensemble means, pin-pointing the area west of North Platte, NE
as one of the favorable spots for convective impacts. FFG's in this
corridor are lower than the neighboring Sand Hill domain, so the
MRGL risk remains relatively small.

...Virginia and North Carolina...

Our surface low will mature and occlude by Tuesday afternoon as the
closed height fields indicate the 850/700/500 mb lows becoming
vertically stacked leading to a slow decay of the surface low by
the second half of the period. Persistent heavy rain potential will
linger across eastern NC up into the VA Tidewater leading to
multi-day totals reaching 2-4" with locally upwards of 6-7" over
the span of 48 hrs. Despite the drier soils leading into the event,
the cumulative effect will lead to areal flooding concerns for
portions of the above locations. Some westerly push of the heavier
QPF is progged in the front half of D2 leading to some areas in
north-central NC up through south-central VA possibly sneaking into
the flash flood threat. The only good news is the weakening surface
low will lead to degrading rates eventually, and slow wane on the
threat. The MRGL risk inherited was maintained with some minor
westerly expansions to account for recent trends in the ensemble means.

Kleebauer


Day 3
Valid 12Z Wed Sep 17 2025 - 12Z Thu Sep 18 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PARTS OF THE
NORTHERN AND CENTRAL PLAINS, SOUTHERN HIGH PLAINS, AND SOUTHEAST FLORIDA...

...Northern and Central Plains...

A strong mid-level shortwave trough will eject into the WY Front
Range and eventually close off across NE generating a maturing lee
cyclone across the Central High Plains. The setup will likely cause
quite a robust deformation signature on the northwest flank of the
cyclone with ensemble mean QPF placement situated over western NE
up through southwestern SD, arcing back into the nose of the warm-
conveyor belt on the northeast side of the system. This is a
classic mid-latitude lee cyclogenesis setup with a strong jet
coupling leading to broad large scale forcing and widespread precip
across the Plains. Eastern side of the cyclone will exhibit the
best convective potential while the deformation axis provides a
solid precip field with moderate to locally heavy rates for several
hrs. in that northwest side of the low. Totals >2" are forecast
within the means across western NE into SD with scattered elevated
QPF across the Missouri River basin located in eastern SD and NE.
This setup is conducive for at least some isolated to scattered
flash flood prospects considering the synoptic evolution. This was
enough to warrant a MRGL risk in those areas deemed the best chance
for heavy rain prospects.

...Southern High Plains...

Maturing lee side low to the north will help drag a trailing cold
front through the Central and Southern High Plains on Wednesday.
The front will slip south and southwest once down near the
latitude of the OK Panhandle, leading to a more textbook backdoor
frontal progression as it enters into the northern TX Panhandle and
northeast NM. Flow begins to run more parallel to the boundary in
these zones when assessing forecast soundings from relevant global deterministic. The key in the setup is a relatively solid
isentropic ascent pattern in a small zone bordering CO/OK/NM/TX
with cross-section views over the area displaying a classic sloped
low-level surface FGEN with strong omega correlating to rapid
ascent as the front progresses through the area. Locally enhanced
corridor of precip will transpire along and in wake of the front
with local maxima of 1.5" to as much as 3" plausible during the
event. This could be enough for an isolated flash flood threat,
especially in those smaller urban areas situated across the 4 state intersection. A MRGL risk has been added to account for the threat.

...Southeast Florida...

Stalled front with an enhanced moisture return across South FL will
lead to a heightened threat for flash flooding over the urban
centers of southeast FL. Deterministic output is scattered in the
exact location of the heaviest precip, ranging from the Keys up to
West Palm Beach and everywhere in-between. The setup is
historically favorable for flash flood concerns over the urban
zones of southeast FL with PWATs hovering between 2-2.3", a solid
1/1.5 deviations above normal. In coordination with the Miami WFO,
a MRGL was maintained for that urbanized coastal corridor between
West Palm down to Miami proper since this is the most likely
location for flash flooding in this type of setup. Will monitor
convective trends as we get closer to see if this necessitates any
expansion, or even a targeted upgrade.

Kleebauer
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