670
FOUS30 KWBC 291900
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Fri Aug 29 2025

Day 1
Valid 16Z 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...

A stationary front lies astride the I-10 corridor from Texas
eastward through the FL Panhandle. Near and south of the boundary,
precipitable water (PW) values were >2 inches (2.26" at LIX at 12Z)
which was around the 90th percentile. Ongoing convection was
slowly sinking southward and eastward which has been responsible
for about 2-5" of rain over the last 6 hours and 1-3" per hour over
recent hours. Latest HREF/REFS guidance still suggests modest
neighborhood probabilities for >5 inches (20-35%) situated across
the aforementioned areas and even the typically much lower EAS
probabilities around 10-15% in some spots. Higher FFG values will
curb the top end of any threat as the recent dry pattern has
relegated all 1/3/6 indices to run very high. Maintained the Slight
Risk from far eastern Texas eastward across southern
Louisiana/Mississippi into Alabama.

Marginal Risk area exists around the Slight Risk area,
encompassing much of northern and eastern Florida where PW values
remain elevated and afternoon convection could support a localized
flooding threat. Small signal for some enhanced rainfall over
northeastern Florida or just offshore.


...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. Leftover mid/upper level moisture from Juliette was
streaming across the region, likely helping increase rainfall
efficiency over the Rockies this morning. CAMs 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, which may limit the
magnitude of the flash flood risk. However, enough of a surge in
instability and PW suggests potential for high rainfall rates
(neighborhood probs of >1" near/over 50%), and enough convective
coverage could support some upscale convective cluster development.
The Slight Risk area was maintained in this region.

Farther 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 where HREF neighborhood probs of
>2"hr exceed 30%. The Slight Risk was maintained here for
localized flooding concerns, with a broader Marginal Risk over the
western High Plains.


...Northeast...

A cold front over NYS will continue eastward this afternoon with a
narrow ribbon of PW values >1-1.25 inches and surface dew points
into the 60s. 12Z CAMs continue to advertise potential for very
localized 1-3 inches of rainfall along the I-95 corridor from ~PVD
northward. The Marginal Risk was maintained in this region.

Fracasso/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...

...20Z Update...

The Slight Risk area across the Plains was expanded southwards into
central 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. 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.

In the Southern Plains, the Slight Risk area was maintained from
eastern New Mexico through the Texas Panhandle and into West Texas
with small adjustments to the shape of the area to account for QPF
trends in the hi-res guidance. 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.

Elsewhere, the broad Marginal was maintained across much of the
Plains and for portions of the Gulf Coast and Southeast.

Dolan

...Previous Discussion...

...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/CENTRAL TEXAS AND FOR EASTERN NEBRASKA...

...20Z Update...

Through collaboration with the Omaha Weather Forecast Office, a
Slight Risk area was introduced for eastern Nebraska, which will
likely see enough instability and moisture to support high rain
rates in isolated to scattered thunderstorms on Sunday. Soils in
this region should also be saturated from heavy rain/storms
expected on Saturday, resulting in a heightened flash flood risk.

The Slight Risk area in Texas was also expanded to include more of
West Texas and a portion of Central Texas. 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
today and Saturday.

The broader Marginal Risk areas for the southern tier and portions
of the Central/Northern Plains and western Midwest were maintained
with small adjustments. The southern Marginal was shifted south to
better align with the forecast frontal position, which will be
responsible for showers and storms along the Gulf Coast and
Florida. Due to the southern shift, a portion of the Central Gulf
Coast and the interior Southeast was removed from the Marginal Risk
area.

Dolan

...Previous Discussion...

Heavy rainfall will continue to focus along a draped frontal
boundary from the Southern Plains to the Southeast. 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


Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt