FOUS30 KWBC 240804
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
404 AM EDT Thu Jul 24 2025

Day 2
Valid 12Z Fri Jul 25 2025 - 12Z Sat Jul 26 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
CENTRAL PLAINS, MIDWEST, AND OHIO VALLEY...

...Central Plains into Ohio Valley...

The combination of robust moisture and the presence of both a
surface low progression out of KS and a slow-moving cold front will
lead to yet another day of heavy rainfall across portions of the
Central Plains into the central part of the Midwest. Guidance has
been struggling to ascertain how the this period will evolve, but
the past 00z NWP has come into a bit better agreement on some of
the ingredients that would lead to another round of heavy rainfall
in-of central and eastern KS and points northeast. The key will be
the migration of the surface low across KS. At this juncture, it's
pretty likely the low center will move into northeast KS by Friday
morning with ongoing convection, potentially with some MCV driven
components that would lead to a relatively active beginning of the
D2. Even if convection trends down for the initial 6hr window,
general diurnal destabilization around the low will lead to another
round of thunderstorm genesis in proximity to the surface
reflection and points northeast. This puts a higher threat for
overlapping days of heavy convection across northeast KS into
northwest MO in the first 12hr period before focus shifts northeast
into IA as the low lifts northeast around the northwestern
periphery of the ridge. Any additional rainfall over the KS/MO area
could spell trouble if the D1 works out to how some of the CAMs are
indicating. The trend is leading to further compromised soils and
perhaps even remnant flooding if another round of heavy rain breaks
out not long after impacts from the previous evening.

The threat for rainfall totals between 2-4" with locally higher
maxima across northeast KS, northwest MO, and southern IA is
gaining steam with an unwavering signal the past 5 runs from the
AIFS ensemble QPF distribution. Granted, convective schema is hard
to pin down at leads, but the synoptic progression would favor
heavy precip across these areas with even some inference of heavy
convection through northern IL and IN thanks to the environment in
place along the front. A SLGT risk was extended back west and
southwest for the growing signal with a high end SLGT forecast
across the aforementioned 3 zones in KS/MO/IA. This period could
have some short term shifts pending convective evolution in the D1,
so stay tuned for future updates.

...Gulf Coast...

The disturbance across the northern Gulf will continue to slowly
migrate to the west with an attendant surface low remaining
situated just south of the west-central Gulf coast. Low center
proxy will be the ultimate factor in the prospects of very heavy
rainfall along the immediate Upper TX coast back into LA. So long
as the low center remains far enough offshore, the greatest low-
level convergence pattern and persistent area of convection could
remain just off the coast to limit impacts. However, the airmass
surrounding the disturbance will still be pretty robust with PWATs
remaining very high (>2.3") for much of the immediate coastal plain
over TX back through the central Gulf coast. The National
Hurricane Center is maintaining a 10% within the latest Tropical
Weather Outlook over the northern Gulf for the next 2-3 days, so
any tropical characteristics from this disturbance could enhance
flash flood prospects further, especially when it moves closer to
the Upper TX coast.

...Northern Plains...

A quick moving shortwave ejecting out of the Rockies is forecast to
impact the Northern Plains on Friday night into early Saturday with
scattered thunderstorms likely to roll through the Dakotas after
sunset. Increased regional PWATs upwards of +2 deviations along
with ample mid-level forcing will be enough for a period of
enhanced heavy rainfall prospects during the time frame of impact. Deterministic output is all over the place in exact convective
placement and magnitude, however signals for 2-4" of rainfall in a
short period of time would be sufficient for at least low-end MRGL
prospects up across parts of the Dakotas. Timing of the shortwave
will be key for the threat, but there was enough consensus on their
being a chance for a maintenance of the MRGL risk inherited.

Kleebauer


Day 3
Valid 12Z Sat Jul 26 2025 - 12Z Sun Jul 27 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE GREAT LAKES, OHIO VALLEY, NORTHERN PLAINS, WESTERN AND CENTRAL GULF
COAST, NORTHEAST CALIFORNIA AND NORTHWEST NEVADA...

...Midwest through Great Lakes...

Disturbance across the Plains will move northeast into the Midwest
and eventually the Great Lakes with heavy rain prospects carrying
through the region. This is marking the end of a persistent heavy
rain setup for the past several days with guidance indicating the
highest potential over IA, northern IL and southern WI. Ensemble
trends have shifted to places along and north of I-80 seeing the
greatest potential for 2+" of rainfall at any point in the D3
period, however there's still some uncertainty on specifics of
where the heaviest core of precip will occur when assessing
individual deterministic, so the current MRGL forecast was
sufficient for this time. That said, there's a good chance we will
see an upgrade at some point in the next series of updates, but
details will need to be ironed out on the previous periods of
convection before initiating the upgrade.

...Gulf Coast...

The remnants of the migrating upper trough and surface low will
remain situated across the western half of the Gulf with the main
area of surface reflection likely coming ashore into TX during the
period. Models are truly all over the place when it comes to the
convective expanse during the D3 time frame with some guidance
having little development to others showing a formidable mass of
precip over LA and the Upper TX coast. In any case, the deep
tropical moisture presence and general instability will be pretty
high across the immediate Gulf coast with the ML outputs relatively
favorable for at least scattered heavy convection along and south
of I-10. In coordination with local WFO's across the central and
western Gulf coast, maintained a MRGL risk with emphasis on the
immediate coastal plain where instability points to more favorable
heavier precip potential.

...Northern Plains...

A second potent shortwave will eject northeast out of the northern
High Plains with another round of heavy precip potential with more
organized convective clusters migrating through the Dakotas.
Signature has bounced around on the exact placement of the multi-
cell organization, but probabilities from the latest NBM and AIFS
Ensemble indicate more of northeastern ND as the primary area of
interest. Look for local 2-3" maxima, at the very least with this
type of setup. The good news is the pattern looks relatively
progressive, so outside some near term mesoscale trends for
repeating cell action, the threat remains firmly in the MRGL risk stance.

...Northeastern California and Northwest Nevada...

Almost a carbon copy of the prior period for convective impacts
lingering across the Northern Sierra up through northeastern CA and
northwest OR. The upper pattern is pretty slow to breakdown with
the diffluent area in the longwave setup still situated over
northern CA into NV. Modest instability and slightly above normal
moisture in the terrain will offer the capability for some isolated
flash flood concerns within any complex terrain and burn scar
remnants in the above area. Precip maxima will be limited to ~1",
so the threat lies within the lower threshold of a MRGL risk, which
is what is now forecast.

Kleebauer
$$
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FOUS30 KWBC 311953
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
353 PM EDT Thu Jul 31 2025

Day 2
Valid 12Z Fri Aug 01 2025 - 12Z Sat Aug 02 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE CAROLINAS AND NORTH/NORTHEAST TEXAS...

...Southeast and Mid-Atlantic...

During this period a potent cold front will be dropping south
through the region in response to a very strong surface high
pressure (above the 99.5th climatological percentile per the
NAEFS) over the Great Lakes/Midwest. This will allow for moisture
to pool along the front and thunderstorms to develop across the
Carolinas on Friday and Friday night. Meanwhile both terrain and
coastal influence are also likely, which may lead to slower storm
motions and heavier rainfall amounts. This combination will also result
in good convective coverage, which will ultimately likely lead to
a decent degree of cell merger activity. Much of the area will have
PW values nearing 2.5 inches along with abundant instability,
resulting in very heavy rainfall rates over 2"/hr in this
thermodynamic environment. Given the likelihood of cell mergers
and westerly mean layer flow nearly parallel to the front, this
should drive an isolated to scattered flash flood risk. 12z HREF
guidance depicted high neighborhood probabilities (60-90%) for at
least 3" in 6-hrs along the coastal Carolinas, where FFG is also
highest. Additionally, along the complex terrain of the western
Carolinas 12z HREF neighborhood probabilities for exceeding 3" in
6-hrs are 40-50%.

Only minor adjustment to the previous outlook was to reduce the
northern portion of the SLGT and MRGL based on southern trends in
the progression of the cold front. Urban areas and the complex
terrain of the southern Appalachians remain most at risk to
scattered instances of flash flooding, with the remainder of the
Carolinas flat and sandy soils capable of soaking in most of the
intense rainfall. The frontal boundary will also linger across the
remainder of the Southeast and into the Lower MS Valley, where
additional instances of flash flooding are possible given weak
steering flow and 2-2.25" PWs. However, most storms should become
outflow dominant and be short-lived after a brief period of intense
rainfall and rates up to 3"/hr.

...Southern Plains...

The cold/stationary front continues to stretch westward towards the
southern Plains along with PW values near 2" Friday into Friday
night. While most activity should remain pulse-like, a surface wave
and meandering MCV could trigger locally heavy rain in
northern/northeast TX Friday night. The location remains somewhat
uncertain, but this area is highlighted by the 12z HREF as having
6-hr probabilities for >5" at 30-40%. Additionally, the RGEM and
ECMWF included elevated QPF values above 2-3" with the 12z runs in
a very similar location. This potential collocated with the
Dallas- Fort Worth metro led to enough confidence for a targeted
Slight Risk. Expect refinements in future outlooks as more CAM runs
become available and/or the MCV at play becomes more trackable.

...Rockies and Plains...

Scattered convection is expected to span from Montana to New Mexico
into Friday. The most favorable environment for heavy rainfall will
likely setup from Montana into the Dakotas, which is where mid
level troughing will be paired with the highest PW anomalies in
the CONUS...above the 90th percentile climatological early August
peak values. Combine this with CAPE forecast around 2000 J/kg and
the environment appears conducive to areas of localized flash
flooding. Hourly rainfall rates up to 1.25-1.5 inches/hour possible
over the Northern Rockies/Montana and up to 2 inches/hour across
the Dakotas. There is also the potential for an MCV across the
Dakotas to provide a focus for locally intense rainfall, but the
location of this heavy rain remains too uncertain for an upgrade to
a Slight Risk. This potential will be evaluated in future outlooks.

Snell


Day 3
Valid 12Z Sat Aug 02 2025 - 12Z Sun Aug 03 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHEAST...

...South and Southeast...

The strong front mentioned will continue pressing southward,
draped from the Southeast westward across the Deep South, Lower
Mississippi Valley and over Texas. High moisture content and
instability along and ahead of the front interacting with the right
entrance region of the upper jet will promote heavy to excessive
rainfall in thunderstorms that could cause localized flash
flooding. Very heavy rainfall rates are expected and should drive
an isolated to scattered flash flood risk. A Slight Risk remains in
effect for portions of the Lowcountry South Carolina, southern
Georgia and far northern/northeast Florida. The front stretching
west across the Gulf Coast states in a moist and unstable
environment could promote scattered diurnal thunderstorms into
Saturday thus maintaining the Marginal Risk.

...Rockies and Plains...

Shortwaves rounding the eastern edge of the upper ridge in the
western U.S. is forecast to interact with the same front that bends
back across the Great Plains, where rounds of rain and
thunderstorms are likely with possibly multiple MCSs. High rain
rates should be supported at times with the above normal moisture
and instability with some areas possibly seeing repeated rounds of
storms as the front begins to lift as a warm front. Location in
heaviest rainfall remains too uncertain for an upgrade to a Slight
Risk at the moment and MCS activity may bode too progressive for
widespread flash flooding, thus the region is covered by a Marginal Risk.

Snell/Campbell
$$
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FOUS30 KWBC 022000
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
400 PM EDT Sat Aug 2 2025

Day 2
Valid 12Z Sun Aug 03 2025 - 12Z Mon Aug 04 2025

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHEAST/GULF COAST AND SOUTHERN PLAINS...

...Southeast/Gulf Coast...
The cold front from Saturday will continue to waver along the Gulf
Coast as a stationary front Sunday in response to subtle
additional height falls as the trough extending from the Northeast
continues to subtly amplify. The trough axis may reach the Gulf
Coast Sunday evening, but flatten at the same time in response to
an elongated ridge draped across the Gulf. Moisture pooled along
this front will remain impressive as PWs remain above 2.25 inches
with deep column saturation noted via moist-adiabatic lapse rates
through the depth of the column indicating tall-skinny CAPE which
is progged to reach above 1000 J/kg during peak heating.
Convergence along the front into these thermodynamics will support
another day of slow moving convection noted by 0-6km mean winds of
just 5-10 kts pointed to the east, with rainfall rates likely
eclipsing 2"/hr at times (HREF 50-60% chance) supported by warm
cloud depths nearing 15,000 ft to produce efficient warm-rain
collision processes.

Late in the aftn and into the evening, a shortwave is progged to
rotate beneath the trough and pivot E/NE from the FL Panhandle into
eastern GA, coincident with a surge in bulk shear up to 35 kts.
This could support some more widespread convection with
organization into clusters/multi-cells. With weak storm motions in
place, any collisions/organization during this time could briefly
pulse up rain rates even more significantly, while also leading to
longer temporal duration or repeating rounds of these rain rates.
Where this occurs, the HREF and REFS both indicate a 70-90% chance
of 3"/24hrs and locally a 40-70% chance of more than 5"/24hrs. This
rain will be falling atop areas that will likely receive
significant rainfall on D1 as well, further enhancing the threat
for flash flooding. Although this region generally takes a lot of
rainfall to flood, the setup appears to support a higher than
typical SLGT risk especially from the FL Panhandle through coastal GA.

Otherwise, scattered thunderstorms with intense rain rates could
produce instances of flash flooding on Sunday. The guidance has a
secondary area of maximum rainfall potential along a westward
advancing surface trough through northern AL into central TN which
may require an upgrade in the ERO with later issuances since
3"/24hr probabilities peak at 40-50%, but this correlated with 3-hr
FFG exceedance that is just 10-15%. At this time opted to maintain
the MRGL risk and re-evaluate with new guidance for a possible
upgrade overnight or on the D1 Sunday.

...Plains...
The elongated stationary front aligned north to south from MT
through TX will weaken Sunday, but leave at least a weak
convergence boundary as it decays. Mid-level flow upstream of this
feature will gradually become more W/NW as it gets squeezed between
an amplifying ridge over the Southwest and a trough across Canada.
Within this pinched flow, multiple shortwaves/vorticity impulses
will shift eastward, interacting with the front to cause another
day of convective development across the High Plains and into the
Plains, with several MCSs possible beneath any of the stronger impulses.

While there is considerable spread and thus uncertainty in the
placement of any of these MCSs, each of them will likely contain
intense rain rates of 1-2"/hr (locally higher) in response to
meridional 850mb flow drawing elevated thermodynamics northward.
From TX to MN a ribbon of PWs of 1.25 to 1.75 inches will overlap a
plume of MUCAPE above 2000 J/kg and bulk shear of 25-35 kts to
support the intense rainfall rates. While the CAMs are generally
suggestive of forward propagating features that will limit the
duration of heavy rainfall, locally any of these could produce some
short-term training, especially where any MCVs and lingering
boundaries can track. Uncertainty is high in where this is most
likely, but the REFS and HREF suggest a slightly higher potential
from north Texas into central KS, as well as across portions of
eastern SD/ND into Minnesota.

The large inherited SLGT risk for TX/OK/KS was cosmetically
adjusted, but further refinements are likely (with a reduction of
category also possible) as confidence in MCS placement becomes more
clear. Across MN, a targeted SLGT risk was considered where HREF
and REFS probabilities for 5"/24 hrs peak above 15% as storms
slow/regenerate beneath a deformation axis downstream of a mid-
level closed low. Confidence is modest across this area, but 24-hr
LPMM from the HREF is 3-4", so FFG exceedance potential appears
higher than surrounding areas. However, there is still a lot of
placement uncertainty among the available models, and some concern
that instability won't be sufficient to support multiple rounds of
heavy rain. While a SLGT risk is still possible with later
issuances, after coordination with WFO DLH opted to maintain the
MRGL risk at this time.

Weiss


Day 3
Valid 12Z Mon Aug 04 2025 - 12Z Tue Aug 05 2025

...THERE ARE MARGINAL RISK AREAS FOR THE NORTHERN ROCKIES, NORTHERN PLAINS/MINNESOTA, AND THE SOUTHEAST...

...Southeast...
Moisture streaming northeast ahead of the longwave trough axis will
maintain unsettled conditions and widespread showers/thunderstorms
from southern AL through GA and coastal SC. There is quite a bit of
uncertainty in the placement of the heaviest axis of QPF on D3
owing to uncertainty in accompanying mid-level impulses progged to
lift out of the Gulf on Monday, and this limits confidence from
upgrading the inherited MRGL risk to a SLGT risk at this time.
However, with PWs likely continuing at 2-2.25 inches overlapping
MUCAPE of more than 1000 J/kg, rainfall rates of 1-2"/hr or more
are likely within any convection that develops and then tracks
northeast. Some repeating rounds are possible, but SREF/GEFS/ECENS probabilities for 3"/24hrs are all quite modest at this time, and
the EC/EC-AIFS is north of the other guidance which could allow the
heaviest rain D3 to not overlap the heaviest rainfall footprint
from D1-2. For these reasons the MRGL risk was maintained and
adjusted, but a SLGT risk may be needed with later issuances.

...Northern Plains...
The closed mid-level low responsible for areas of heavy rainfall
Sunday will continue to lift northeast and weaken on Monday. The
weakening of this feature will result in less ascent, but a
lingering boundary in its wake could still produce enhanced low-
level convergence, primarily across Minnesota. The threat for
heavy rainfall appears lower D3 than D2, as both ascent and
thermodynamics are reduced, but locally rainfall rates in excess of
1"/hr are possible, with a secondary surge in convection possible
late in response to 850mb winds reaching 20-30 kts converging into
the region. With FFG likely to be lowered from antecedent rainfall
D1 and D2, isolated excessive rainfall impacts will again be
possible on Monday.

...Northern Rockies...
A shortwave moving northeast across ID/MT will help amplify a
trough shifting into the Northern High Plains on Monday. This will
drive enhanced ascent into the already broad synoptically forced
lift, helping to spawn a weak wave of low pressure tracking into
the High Plains the latter half of D3. Low-level southeasterly flow
will draw elevated PWs and MUCAPE into the region aiding a
moistening column from high-level SW flow emerging from the
Pacific. The result of this will likely be showers and
thunderstorms moving progressively eastward from the Northern
Rockies through the northern High Plains. With PW anomalies +1 to
+1.5 sigma above the climo mean, rainfall rates may reach 1"/hr at
times, which despite the anticipated progressive nature of these
cells, could produce isolated impacts due to runoff.

Weiss
$$
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FOUS30 KWBC 090755
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
355 AM EDT Sat Aug 9 2025

Day 2 Valid 12Z Sun Aug 10 2025 - 12Z Mon Aug 11 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FROM EASTERN
KANSAS NORTHEAST THROUGH SOUTHERN WISCONSIN...

...Central Plains through the Upper Midwest...
An extremely active pattern continues across the Plains and Upper
Midwest as the synoptic regime from D1 persists through the weekend.

An amplifying mid-level trough centered from ND through NM will
deepen to produce 500mb heights that may locally fall below the
10th percentile according to NAEFS. ALthough the primary vorticity
maxima in the core of the trough spins northeast into Ontario,
lingering impulses shedding back into the Four Corners maintain the
trough axis back to the west. This will persist mid-level SW flow
angling across the Central Plains and into the Upper Midwest, with
weak impulses rotating through the flow and persistent upper
diffluence within the RRQ of a poleward arcing jet streak
downstream of the primary trough axis providing deep layer ascent.
This pattern matches the conceptual model for a Maddox Frontal
rainfall event, and another day of heavy rainfall is likely Sunday
in portions of the region.

As the synoptic pattern stalls, a surface stationary front will
oscillate from WI through OK, providing a focus for convective
generation along the low-level convergent boundary. Additionally,
any weak impulse transiting the front could result in weak low-
pressure development along the boundary. This makes for a
challenging QPF and ERO forecast since the environment will be
extremely favorable for training heavy rainfall, but the exact
placement remains very much uncertain.

As far as the environment, thermodynamics are expected to be
exceptional for the area supporting intense rainfall rates. PWs
above 2", or well above the 90th percentile, are progged to surge
northward on return flow ahead of the front, combining with MUCAPE
of 2000 J/kg to fuel widespread convective development as the
850mb inflow/LLJ propagates northeast. Mean 0-6km winds will again
be parallel to the boundary, although with wind speeds are expected
to be generally more progressive than on Saturday, reaching 15-20
kts. However, bulk shear progged to reach 40 kts will support
organized cells, and Corfidi vectors collapsed to just 5 kts and
aligned against the mean wind indicate a high threat for
backbuilding cells leading to longer duration of heavy rainfall and
slow net cell motions. With rainfall rates of 2-3"/hr expected,
this could result in axes of 3-5 inches of rain with locally higher
amounts. This will likely result in scattered to numerous flash
flood instances, with locally significant impacts possible should
heavy rain train across urban areas.

There remains uncertainty into the placement of the heaviest
rainfall, and the inherited MDT risk was adjusted cosmetically for
the recent guidance to align both with the highest REFS/SREF
exceedance probabilities while also accounting for the expected
heavy rainfall footprint from D1. Additionally, some adjustments
were made to better reflect the CSU first guess field which pulled
the higher risk areas a bit SW from previous runs.

...Southwest...
A MRGL risk remains for portions of the Southwest on Sunday as
monsoonal moisture begins to return to the area leading to a more
active convective pattern. A mid-level trough extending down from
the Northern High Plains will continue to amplify Sunday, producing
lowered heights across the Four Corners and Desert Southwest,
through which weak spokes of vorticity will rotate. These lowered
heights and locally enhanced ascent will impinge into an
increasingly favorable thermodynamic environment to support
convection with heavy rainfall. Low-to-mid level flow will
gradually back more to the SW, allowing for a better draw northward
of PWs exceeding 1", which may spread as far north as the Mogollon
Rim and combine with MUCAPE of 500-1000 J/kg across the southern
half of AZ and NM. This will support scattered to widespread
showers and thunderstorms which will move slowly eastward through
the day. With rainfall rates as much as 1"/hr at times, this could
result in at least isolated instances of flash flooding, especially
across more vulnerable soils or terrain, and the MRGL risk was
maintained and adjusted for new guidance.

...Southeast...
Another very active day across portions of the Southeast is
expected as tropical moisture (PWs above 2.25 inches) persists in
response to a wave of low pressure drifting across the eastern
Gulf. The mid-level pattern remains quite diffuse into Sunday, with
a col sitting over much of the Southeast in response to broad
ridging along the Atlantic Seaboard. This suggests that features
will move little during the period, and guidance indicates a weak
shortwave drifting along the GA/SC coast once again on Sunday.

850mb inflow from the southeast will maintain impressive moist
advection onshore, and this wind, while modest at 15-20 kts, will
generally exceed the mean 0-6km winds which will be just 5-10 kts.
This will provide a two-pronged effect on the heavy rainfall threat
in that the 850mb wind exceeding the mean wind will drive large
scale enhanced ascent, while the weak mean winds will additionally
support slow movement of convection that develops. With rainfall
rates likely peaking at 2-3"/hr (30% chance for 2"/hr from the
HREF), maximum rainfall of 3-5" with locally higher amounts is
again possible on Sunday as reflected by SREF/GEFS/HREF/REFS
probabilities. Some of this may fall atop soils that are sensitive
from prior heavy rainfall on Friday and Saturday, leading to a
locally higher flash flood risk. The latest UFVS CSU First guess
field has a SLGT risk over coastal SC, which overlaps almost
identically with the SLGT risk on D1 and the highest REFS/HREF/GEFS probabilities into D2 (when available). For this reason a targeted
SLGT risk was again added, primarily for the SC coastal plain.

Weiss


Day 3 Valid 12Z Mon Aug 11 2025 - 12Z Tue Aug 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM NORTHERN
MISSOURI THROUGH NORTHERN ILLINOIS AND SOUTHERN WISCONSIN...

...Central Plains through the Great Lakes...
The amplifying trough across the High Plains and the accompanying
cold front producing the heavy rainfall across the Plains/Upper
Midwest Saturday and Sunday will gradually pivot eastward on D3
/Monday/. Despite this eastward translation, pinched 850-500mb flow
between this trough and a ridge to the east will maintain efficient
moist advection out of the Gulf, albeit with PW anomalies lower
than forecast for the weekend. This suggests that another day of
training convection is likely along the front from Oklahoma
through Michigan, but with somewhat reduced intensity. Rainfall
rates will likely still peak above 1"/hr at times, which through
training could produce 1-3 of rainfall (ECENS/GEFS probabilities
for 3+ inches below 10%), and where this rain overlaps with heavy
rain from the weekend (most likely on the western edge of the SLGT
risk area), scattered instances of flash flooding are possible.
Otherwise, any cells training along the front could produce
isolated responses and a broad MRGL risk draped along the length of
the front into the southern High Plains continues.

...Southeast...
Rinse and repeat for the Southeast, especially in the vicinity of
South Carolina, Georgia, and the Florida Panhandle, as onshore
return flow around an elongated high over the Atlantic spreads
tropical moisture onshore. PWs are again progged to be 2-2.25
inches with overlapping MUCAPE of 1000-2000 J/kg. Within these
impressive thermodynamics, forcing for ascent will be provided both
by land/sea convergence axes but also downstream of two
shortwaves: one moving near the SC coast and a second rotating
northward from the Gulf into the FL Panhandle. Both of these mid-
level features may reflect to the surface as inverted troughs,
providing additional convergence for slow moving thunderstorms
containing rainfall rates of 1-3"/hr. There is quite a bit of
spread among the global ensembles by D3 as to how far inland
convection will track, and as to whether there will be any focused
areas of heavier rainfall. For these reasons a broad MRGL risk
remains across the area for at least isolated flash flood
potential, especially since soils will be primed from heavy
rainfall anticipated on D1 and D2.

Weiss
$$
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FOUS30 KWBC 100835
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
435 AM EDT Sun Aug 10 2025

Day 2 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 THROUGH THE UPPER MIDWEST, AND THE COASTS OF THE CAROLINAS...

...Central Plains through the Great Lakes...
The anomalous trough drifting slowly eastward from the High Plains
will weaken slightly as heights rise across the Central Plains
Monday. This will have limited overall affect on the downstream
rainfall, however, as spokes of vorticity embedded within the flow
and the accompanying surface front remain in place to drive ascent,
with only slow eastward advance expected through D2.

Despite this eastward translation, pinched 850-500mb flow between
this trough and a ridge to the east will maintain efficient moist
advection out of the Gulf, albeit with PW anomalies lower than
forecast for the weekend (PWs around 1.75 inches or 0.5 to 1.0
standard deviations above the climo mean). This suggests that
another day of training convection is likely along the front from
Oklahoma through Michigan, but with somewhat reduced intensity from
prior days. Another challenges for D2 is the uncertainty in frontal
position and convective timing, as lingering boundaries from
Sunday's convection (with additional uncertainty in placement) will
play an important role into the training potential and heavy rain
axes on Monday. This suggests that despite a still favorable
synoptic pattern and elevated thermodynamics, the SLGT risk remains
the highest needed category for the D2 ERO.

On Monday, rainfall rates will likely still peak above 1"/hr at
times, which through training could produce 1-3 of rainfall
(ECENS/GEFS probabilities for 3+ inches below 10%), and where this
rain overlaps with heavy rain from the weekend (most likely on the
W/SW edge of the SLGT risk area), scattered instances of flash
flooding are possible. Otherwise, any cells training along the
front could produce isolated responses and a broad MRGL risk draped
along the length of the front into the southern High Plains continues.

...Southeast...
Yet another active day across the Southeast is expected Monday as
an inverted low-to-mid level trough drifts northeast along the
coast of the Carolinas. This trough will move within a favorable
thermodynamic environment characterized by still highly anomalous
PWs of 2 to 2.25 inches, although the slow retreat of the mid-level
ridge to the east should help ease some of this moisture the latter
half of D2. Still, the overlap of these elevated PWs with MUCAPE of
1000-2000 J/kg will support convection with heavy rainfall.

In general, convection across the Southeast on Monday should be
scattered in coverage, but some organization, or at least better
clustering, is likely in the vicinity of any shortwaves and the
inverted trough, primarily from the Grand Strand of SC to the
Crystal Coast of NC. Here, repeating rounds of convection with
efficient rain rates exceeding 2"/hr are likely, driven by
impressive low-level confluence. Elsewhere across the Southeast,
heavy rainfall rates are also likely, but with less organization,
but still slow storm motions. The rainfall probabilities for more
than 3" peak along the SC/NC coasts and the SLGT risk was adjusted
cosmetically for the new guidance. Otherwise, a broad MRGL risk
continues for slow moving thunderstorms across areas that have had
recent heavy rainfall, and an expansion was made into the Upstate
of SC where some of the high res CAMs suggest enough upslope to
enhance rainfall locally in that area.

Weiss


Day 3 Valid 12Z Tue Aug 12 2025 - 12Z Wed Aug 13 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER MIDWEST/GREAT LAKES, THE SOUTHWEST, AND GULF COAST/SOUTHEAST...

...Upper Midwest...
The anomalous mid-level trough that will produce the heavy rainfall
D1 and D2 across the Upper Midwest/Central Plains will weaken
Tuesday as shortwaves embedded within the trough become more
rapidly absorbed into westerlies across the northern tier of the
CONUS. A lingering shortwave trough, likely convectively enhanced,
pivoting across KS/MO will drive sufficient ascent for additional
rainfall along the weakening front, but with lesser moisture and
instability than was available earlier in the week. Still, at least
short term training of intense rainfall rates is likely as mean
layer winds align to the weakening front, which could result in
isolated instances of flash flooding.

...Southeast...
Elongated mid-level ridge extending westward from the Atlantic to
along much of the Gulf Coast will subtly retreat Tuesday as a
shortwave emerging from the Gulf lifts northward. The modest height
falls and PVA accompanying this feature will drive ascent into an
otherwise weakly forced environment, producing a favorable setup
for scattered to numerous thunderstorms from the central Gulf Coast
northeast along the periphery of the ridge into Georgia.
Thunderstorms that develop will contain heavy rainfall rates of
1-2"/hr in response to favorable thermodynamics characterized by
PWs of 2-2.25 inches overlapping MUCAPE as high as 2000 J/kg. The
general SW return flow will push storms along steadily to the N/NE,
but with repeating rounds possible and some organization beneath
the shortwave, a few instances of flash flooding could result as
rainfall reaches 2-3" in some areas.

...Southwest...
Mid-level ridging will expand but shift subtly westward on Tuesday
while weak impulses rotate around its periphery. This will help to
intensify instability across the region, and progs indicate a
larger plume of 1000 J/kg MUCAPE spreading across the southern
portions of AZ and NM, especially during peak aftn heating. This
will combine with PWs that will be above 1" in many areas south of
the Mogollon Rim, leading to a favorable environment for
convection. Where any of these impulses rotate aloft, enhanced
ascent will yield scattered to widespread thunderstorms with rain
rates approaching 1"/hr at times, and these storms will move
slowly/chaotically beneath the ridge. This could result in
isolated instances of flash flooding, most likely where any storms
track across more vulnerable terrain features or burn scars.

Weiss
$$
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FOUS30 KWBC 102016
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
416 PM EDT Sun Aug 10 2025

Day 2 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 THROUGH THE UPPER MIDWEST, THE COASTS OF THE
CAROLINAS, & THE FLORIDA PANHANDLE...

...Southern Plains & MO-KS-AR-OK...

The South Central U.S. will be sandwiched between two upper level
disturbances; one upper trough approaching from the Southern
Rockies, and mid-upper level trough axis over southern Texas. Atop
the atmosphere, modest diffluent 250mb flow will support divergence
aloft while a nearby surface frontal boundary acts as a trigger
for thunderstorms. Any residual outflow boundaries from Sunday
night's convection or from Monday afternoon's convection will also
likely play a role in firing off thunderstorms to the south and
east of the surface front. PWATs will generally be >1.8" along the
Red River and points north and east, while areas as far west as
the TX Panhandle and cap rock are between 1.4-1.6". In terms of
instability, lesser values (MLCAPE 500-1,000 J/kg) will be
available in the TX Panhandle, with greater over the MO-KS-AR-OK
region through Monday night. The 12Z HREF does show spotty areas of moderate-chance probabilities (40-60%) within the Slight Risk area
for >3" of rainfall, as well as low-chance probabilities (10-30%)
for >5" in central OK. Given these factors, the Slight Risk was
focused more here compared to the previous forecast cycle.

...Middle MS Valley...

The Slight Risk was scaled back here given the reduction in
available instability, latest QPF reduction, and lesser footprint
of >3" rainfall probabilities in the 12Z HREF. With soils growing
more saturated and the lingering presence of near 2" PWATs, there
is still a localized flash flood threat, hence the presence of a
rather large Marginal Risk area that stretches from the I-70
corridor from KS/MO on north through the Great Lakes.

...Florida Panhandle & Big Bend...

In coordination with TAE, introduced a Slight Risk for areas along
and south of I-10 in the FL Panhandle and Big Bend. As a mid-to-
upper level inverted trough axis approaches, it will be accompanied
by a wealth of anomalous PWATs that will approach 2.5" in some
areas. Modeled soundings show warm cloud layers just shy of
16,000ft deep in some cases with little-to-no capping inversions
Monday afternoon. On the eastern flank of the inverted trough,
925-850mb winds will be uniformly out of the SE. ECMWF soundings
over the Big Bend show Corfidi Upshear vectors that are <10 knots
Monday afternoon, suggesting the potential for back-building and
training thunderstorms. Given the abundance of tropical moisture
and MLCAPE up to 1,000 J/kg, it is quite possible to have
thunderstorms generate 2" of rainfall in as little as 30 minutes.
The scale of these storms are making QPF forecasts across CAMs
guidance widely varying on location, but the atmospheric parameters
support an increasingly concerning setup for flash flooding for Monday.

Mullinax

---Previous Discussion---

...Southeast...
Yet another active day across the Southeast is expected Monday as
an inverted low-to-mid level trough drifts northeast along the
coast of the Carolinas. This trough will move within a favorable
thermodynamic environment characterized by still highly anomalous
PWs of 2 to 2.25 inches, although the slow retreat of the mid-level
ridge to the east should help ease some of this moisture the latter
half of D2. Still, the overlap of these elevated PWs with MUCAPE of
1000-2000 J/kg will support convection with heavy rainfall.

In general, convection across the Southeast on Monday should be
scattered in coverage, but some organization, or at least better
clustering, is likely in the vicinity of any shortwaves and the
inverted trough, primarily from the Grand Strand of SC to the
Crystal Coast of NC. Here, repeating rounds of convection with
efficient rain rates exceeding 2"/hr are likely, driven by
impressive low-level confluence. Elsewhere across the Southeast,
heavy rainfall rates are also likely, but with less organization,
but still slow storm motions. The rainfall probabilities for more
than 3" peak along the SC/NC coasts and the SLGT risk was adjusted
cosmetically for the new guidance. Otherwise, a broad MRGL risk
continues for slow moving thunderstorms across areas that have had
recent heavy rainfall, and an expansion was made into the Upstate
of SC where some of the high res CAMs suggest enough upslope to
enhance rainfall locally in that area.

Weiss


Day 3 Valid 12Z Tue Aug 12 2025 - 12Z Wed Aug 13 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER MIDWEST/GREAT LAKES, THE SOUTHWEST, AND GULF COAST/SOUTHEAST...

2030Z Update...

There were some minor adjustments made this forecast cycle to the
Marginal Risk areas based on latest 12Z guidance and WPC QPF. The
Southeast will be closely monitored given the same feature
supporting a Slight Risk on Day 2 in the FL Panhandle and Big Bend
areas will move farther inland on Tuesday. However, there remains a
fair amount of spread regarding how much rainfall occurs and which
areas are favored. Given the lingering uncertainty, opted to
hold on to a Marginal Risk area with no upgrade this forecast cycle.

Mullinax

---Previous Discussion---

...Upper Midwest...
The anomalous mid-level trough that will produce the heavy rainfall
D1 and D2 across the Upper Midwest/Central Plains will weaken
Tuesday as shortwaves embedded within the trough become more
rapidly absorbed into westerlies across the northern tier of the
CONUS. A lingering shortwave trough, likely convectively enhanced,
pivoting across KS/MO will drive sufficient ascent for additional
rainfall along the weakening front, but with lesser moisture and
instability than was available earlier in the week. Still, at least
short term training of intense rainfall rates is likely as mean
layer winds align to the weakening front, which could result in
isolated instances of flash flooding.

...Southeast...
Elongated mid-level ridge extending westward from the Atlantic to
along much of the Gulf Coast will subtly retreat Tuesday as a
shortwave emerging from the Gulf lifts northward. The modest height
falls and PVA accompanying this feature will drive ascent into an
otherwise weakly forced environment, producing a favorable setup
for scattered to numerous thunderstorms from the central Gulf Coast
northeast along the periphery of the ridge into Georgia.
Thunderstorms that develop will contain heavy rainfall rates of
1-2"/hr in response to favorable thermodynamics characterized by
PWs of 2-2.25 inches overlapping MUCAPE as high as 2000 J/kg. The
general SW return flow will push storms along steadily to the N/NE,
but with repeating rounds possible and some organization beneath
the shortwave, a few instances of flash flooding could result as
rainfall reaches 2-3" in some areas.

...Southwest...
Mid-level ridging will expand but shift subtly westward on Tuesday
while weak impulses rotate around its periphery. This will help to
intensify instability across the region, and progs indicate a
larger plume of 1000 J/kg MUCAPE spreading across the southern
portions of AZ and NM, especially during peak aftn heating. This
will combine with PWs that will be above 1" in many areas south of
the Mogollon Rim, leading to a favorable environment for
convection. Where any of these impulses rotate aloft, enhanced
ascent will yield scattered to widespread thunderstorms with rain
rates approaching 1"/hr at times, and these storms will move
slowly/chaotically beneath the ridge. This could result in
isolated instances of flash flooding, most likely where any storms
track across more vulnerable terrain features or burn scars.

Weiss
$$
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FOUS30 KWBC 140754
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
354 AM EDT Thu Aug 14 2025

Day 2 Valid 12Z Fri Aug 15 2025 - 12Z Sat Aug 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
MINNESOTA AND WISCONSIN...

...Upper Mississippi Valley...
A cold front will progress slowly eastward Friday across Minnesota,
elongated from Wisconsin to South Dakota by the end of D2. This
front will elongate and pivot more to a W/E direction as the
driving mid-level flow gets squeezed between a trough over northern
Canada and a bulging ridge across the Lower/Mid Mississippi Valley.
As the flow becomes more zonal to align elongate the front, waves
of vorticity will surge eastward within the pinching flow to track
west to east along this front from the Dakotas into Wisconsin. This
will produce enhanced lift into an environment that will steadily
become more favorable for convection, and may feature extreme
thermodynamics of PWs above 1.75 inches overlapping MUCAPE of
3000-4000 J/kg later D2.

This suggests that thunderstorms will become scattered to
widespread, peaking later in the day as the LLJ ramps up to 25-35
kts from the SW. This will occur concurrently with a surge of bulk
shear to above 35 kts, and as warm cloud depths climb during this
period as well, convection will grow upscale, potentially into one
or more MCS, with rainfall rates of 1-3"/hr. Mean 0-6km winds of
15-25 kts suggest cells will move quickly eastward, but
redevelopment along the front and any upwind growth on MCS
boundaries could prolong this rainfall through
backbuilding/training. The inherited MRGL risk was modified
cosmetically and a targeted SLGT risk was added to match the
highest ensemble probabilities of 3 inches which also overlap some lower FFG.

...Mid-Atlantic through portions of the Southeast...
The cold front from Thursday will dissipate into a trough Friday
while pushing south towards AL/GA/SC. Despite the weakening of this
boundary and increasing heights aloft in the vicinity of an
expanding mid-level ridge, showers and thunderstorms are again
expected, although in a more scattered fashion than on Thursday.
PWs will remain elevated as tropical moisture continues across the
region, exceeding 2 inches in a ribbon from eastern NC through the
Gulf Coast of MS/LA. This will overlap with impressive MUCAPE above
2000 J/kg during peak heating to drive aftn convection, generally
of a pulse nature, across much of the region. Weak impulses are
modeled within the flow, but with minimal accompanying height falls
or PVA, so any organization will be tied to outflow boundaries or
storm mergers within the otherwise pulse environment. Despite
rainfall rates that will likely peak at 2-3"/hr thanks to the
robust thermodynamics, short lifespans and a lack of organization
suggests only a MRGL risk of excessive rainfall is needed.

...Southwest...
The flow across the Southwest on Friday becomes increasingly
pinched between an amplifying trough digging over California and a
bulging ridge centered near the Central Plains. Shortwave energy
and accompanying spokes of vorticity will periodically shed from
this upstream trough and track SW to NE from southern AZ through
the Four Corners, likely resulting in widespread convective
development, especially as a MUCAPE plume surges above 1000 J/kg.

It is possible that development will be slow to initiate on Friday
due to remnant overnight convection Thursday night leaving cloud
cover early, but most available models including the GFS-forced UA
WRF indicate widespread thunderstorms from southern AZ through
UT/CO and even into WY during the evening. Rainfall rates in
convection will likely peak above 1"/hr across AZ where
instability/PWs are higher, but should reach 0.5"-1"/hr elsewhere.
While 0-6km mean winds will be progressive enough to limit
individual cells from producing too much rain, sufficient bulk
shear of 20-30 kts, especially beneath any shortwave impulses, will
help organize convection into clusters to either lengthen rainfall
duration or result in repeating rounds of storms. Where this
occurs, rainfall probabilities above 1" reach as high as 30-40%,
and the MRGL risk was expanded northward from inherited.

...Western Gulf Coast...
Invest 98L and its accompanying potent mid- level circulation will
lift northwest into northern Mexico or southern Texas Friday
afternoon. To the east of this feature, accelerating low-to-mid
level winds will advect a plume of tropical moisture northward onto
the Texas coast, with PWs potentially exceeding 2.25 inches along
much of the Texas coast. While this is only around the 90th
percentile from the CFSR climatology, it will be accompanied by
MUCAPE exceeding 3000 J/kg drawn inland by 850mb winds of 20-30 kts
(equal to or greater than the mean 0-6km wind). Although the
deterministic models feature a wide variation in QPF output Friday,
and the resulting ensemble probabilities are suppressed in
response, it appears the setup is favorable for at least modest
inland penetration of training heavy rainfall within thunderstorms,
so a MRGL risk was added for portions of the region.

...Pacific Northwest...
The core of a rare August atmospheric river (AR) will move onshore
WA state on Friday, leading to prolonged heavy rainfall, continuing
from the landfall on Thursday and discussed in the D1 ERD. While
QPF will likely be greater on Friday (potentially 2-4" and even
locally greater in the higher terrain of the Olympics and northern
Cascades), the threat for excessive rainfall remains somewhat
uncertain. Impressive PWs of 1.25 to 1.5 inches (locally the
highest ever recorded in the 5-week CFSR climatology from NAEFS)
and formidable 850mb winds will help drive strong upslope ascent
supporting this intense rainfall into upwind terrain features.
While it is nearly certain rainfall will be heavy, there is less
certainty into whether rain rates can be sufficient to cause rapid
runoff atop very dry soils since MUCAPE is forecast to be
negligible which should keep rain rates to around 0.5"/hr. If this
rain were to fall atop recent and sensitive burn scars, instances
of flash flooding could result, but at this time the threat appears
to be below 5% when considering the climatology of the event as
well. After coordination with WFO SEW and OTX, other than some
concern about a few sensitive burn scars, agreement was made on
keeping a MRGL risk out of the forecast at this time.

Weiss


Day 3 Valid 12Z Sat Aug 16 2025 - 12Z Sun Aug 17 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE UPPER
MIDWEST INTO THE GREAT LAKES...

...Central Plains through the Great Lakes...
Pinched mid-level flow will become increasingly squeezed between a
trough over Ontario and a ridge expanding from the Gulf Coast.
Between these two features, nearly zonal flow will force a cold
front to generally align west to east and stall, providing a
convergent impetus for convection. Along this front, spokes of
vorticity will track west to east leading to locally enhanced
ascent to support waves of low pressure, while 850mb inflow returns
around the high pressure ridge and reaches 25-35 kts to draw
elevated thermodynamics characterized by PWs above 1.75 inches and
MUCAPE of 4000 J/kg into the boundary. This will support multiple
rounds of thunderstorms through the day, peaking during the
evening/Saturday night, with rainfall rates of 1-2"/hr or more at
times, leading to scattered instances of flash flooding. A SLGT
risk has been added for portions of this area where probabilities
from the SREF/GEFS/ECENS align for more than 3" of rain.

...Southwest...
Continued S/SW mid-level flow around the periphery of a ridge
positioned over the Mississippi River Valley will maintain elevated
moisture into the Southwest on Saturday. Guidance continues to
suggest that weak shortwaves/vorticity maxima will lift northeast
embedded within the flow, although the intensity of these features
is generally modest, and weaker than on Friday. Additionally,
although 850mb flow will remain southerly over NM, it is progged to
shift a bit more to the west over AZ, lowering the overall PW
anomalies and indicating the greater risk for any isolated flash
flooding will shift east from prior days. MUCAPE of 500-1000 J/kg
will support rainfall rates that may approach 1"/hr at times, and
if these fall across more sensitive features like burn scars or
urban areas, isolated instances of flash flooding could result.

...Southeast...
A wave of low pressure along a weakening cold front will drift
southeast away from the NC coast on Saturday. At the same time, a
building ridge over the Mississippi River Valley will lead to
anti-cyclonic mid-level flow out of the NW into the Southeast,
setting up a situation with moist confluent flow intensifying over
the region. PWs will likely remain elevated above 2" along the Gulf
Coast, but be lower elsewhere as drier air tries to advect from the
NE around the offshore low, and this will result in less widespread
coverage of thunderstorms than prior days. While coverage of
convection is expected to generally be scattered, some locally
enhanced rainfall along any convergence axes is possible due to
rainfall rates that will still reach 1-2"/hr at times. Where these
fall across vulnerable soils from widespread convection on prior
days, impacts could result, and a MRGL risk continues for portions of the area.

Weiss
$$
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FOUS30 KWBC 210719
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
319 AM EDT Thu Aug 21 2025

Day 2 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...

...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 areal average of ~2-3" of precip currently forecast
across southern SC through much of southeastern GA.

The most robust signal was within the probabilities for FFG
exceedance just based off the 12-00z window on Fri/Sat indicating

60% chance of both 3hr and 6hr FFG exceedance probabilities

centered from Charleston, SC down through the SC Low Country into
far southeast GA. This includes the Savannah, GA area, a place more
prone to flash flooding due to its urbanization factors. This will
be a common theme in the flash flood prospects with this setup as
heavy rainfall will develop further inland in proximity to the
front leading to even inland areas of GA seeing a greater threat
for localized flooding than usual. Rates will be pretty stout
considering the environmental factors in place when you couple
1500-2500 J/kg SBCAPE with deep layer moisture being forecast from
the sfc to near the tropopause. This is a 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 if the PWATs in a given area get up towards
that 2.5" marker. Even with the higher FFG's in place, the signal
for enhanced convective rainfall output and flash flood concerns
are worthy of a higher risk compared to the previous forecast. In
coordination with local WFOs across SC and GA, a SLGT risk upgrade
is now in effect for the period beginning Friday AM, likely
carrying into early Saturday AM.

...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" PWATs 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. 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.
Consistent signal in the means and modest probabilities within the
beginning of the convective window on the end of the 00z HREF were
satisfactory for maintaining continuity in the current MRGL risk
outlined. Thus, little change was necessitated from the previous forecast.

Kleebauer


Day 3 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 PWATs will linger across the Southeastern CONUS through
the first half of the weekend as the stalled frontal positioning
will lead to sustained moisture pooling within the confines of the
boundary. Increasing meridional component upstream over the
Midwest/Ohio Valley will lead to a modest surge in moisture along
the Appalachian front from GA up through WV 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 if the conditions are
truly compromised considering the plethora of rain forecast in the
D2. The trend is 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...

A relative repeat in the setup from D2 will yield widespread
convection across southern and eastern CA 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. thanks to forecasted vorticity maxima sliding down the
eastern flank of the ridge and providing focused ascent over the
aforementioned terrain. Areas in the more prone slot canyon, burn
scar remnants, and dry washes will once again be the target of
interest for flash flood prospects allowing for a broad MRGL risk
placement to account for the threat. Pending evolution of guidance
and perhaps more focused areas of concern in the range of CAMs, an
upgrade could very well be plausible in future updates.

Kleebauer
$$
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FOUS30 KWBC 260802
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
402 AM EDT Tue Aug 26 2025

Day 2
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 30-45 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. Latest guidance has continued to
trend wetter in the central High Plains and even along the
foothills of the Central Rockies, leading to an expansion of the
Slight Risk into northern CO and southeast WY. But the greatest
concern lies over southern Kansas where even 75th percentile 24-hr
QPF on the NBM is topping 5". This setup bears watching as locally
significant flash flooding cannot be ruled out in parts of southern
and eastern KS, northeast OK, and southwest MO.

...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. There is increasing confidence in enough
instability (500-1,000 J/kg MUCAPE) 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 inherited 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 on Wednesday.

Mullinax


Day 3
Valid 12Z Thu Aug 28 2025 - 12Z Fri Aug 29 2025

...THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL PLAINS & 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 a healthy amount of 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 MUCAPE 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, but even as far east as MS/AL and as far west as central
OK could also be at-risk for flash flooding on Thursday.

...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. A potential
categorical risk upgrade may be necessary in the northern Rockies,
but it will come down to how much instability is available and what
the state of antecedent soil moisture conditions are following
Tuesday and Wednesday's rainfall.

Mullinax
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