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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


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