FOUS30 KWBC 030828
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
428 AM EDT Sat May 3 2025

Day 1
Valid 12Z Sat May 03 2025 - 12Z Sun May 04 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE GULF
COAST REGION INTO PARTS OF THE NORTHEAST AND THE SACRAMENTO 
MOUNTAINS OF NEW MEXICO

A slow moving mid- and upper-level circulation is expected to form
later today within a broader mid/upper level trough digging
eastward. With low level flow drawing deeper moisture northward
ahead of the system...thunderstorms that form along and immediately
east of a surface cold front will be moving into an environment of
supporting locally heavy rainfall rates and amounts over portions
of the Ohio Valley southward towards the Gulf coast today and from
portions of southern New England southward towards the Carolinas
and areas in and near the southern Appalachians where deeper
moisture resides this afternoon and evening, The 03/00Z suite of 
numerical guidance hint that there could be some 1 inch to perhaps 
2 inch amounts where frontogenetic forcing aligns favorably in 
between the Gulf and the Ohio Valley...but the signal for excessive
rainfall appeared tempered by the progressive nature of the 
forcing and confidence was limited by the lack of run to run / 
model to model consistency with placement of highest model QPF.

Maintained the previously issued Marginal Risk area in New Mexico
given the antecedent conditions after the rain on Friday and the
sensitivity over/near burn scars in the southeast portion of the state.

Bann


Day 2
Valid 12Z Sun May 04 2025 - 12Z Mon May 05 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE
EASTERN UNITED STATES AND SOUTHERN ROCKIES AND ADJACENT HIGH PLAINS...

The risk of excessive rainfall persists across parts of the Mid-
Atlantic and Southeast US as a slow moving closed low embedded 
within a broader upper trough continues to make its way eastward. Deepest
moisture of 1.25 to 1.5 inches will be eventually be shunted off- 
shore late in the period. Until then...isolated downpours are 
possible with spaghetti plots of 2 and 3-inches of rain in 24 hours
mainly being produced by models with the ARW core...but enough 
members from the NMM core and from the GEFS to warrant a Marginal.
The western boundary of the Marginal was trimmed compared with the
previous outlook given the models being more progressive with the
surface cold front and the push of drier air being brought in
behind the front.

There is also a Marginal Risk area over parts of New Mexico again
as moisture continue to spread northward and westward from the
Gulf. After 00Z...the flow aloft between the westerly subtropical
jet and a jet streak and low- and mid-levels become increasingly
diffluent with height falls beginning ahead of an approaching
closed low from the west. This...along with moisture and a low
level boundary already in place...should support late day and
evening storms that may produce locally heavy rainfall rates.

Bann


Day 3
Valid 12Z Mon May 05 2025 - 12Z Tue May 06 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE HIGH PLAINS ADJACENT TO THE SOUTHERN ROCKIES...

Shortwave energy rotating around the periphery of an upper low
making its way over the Southwest US will trigger late day
thunderstorms on Monday over parts of West Texas that grow upscale
in terms of both coverage and rainfall amounts through much of
Monday night/early Tuesday morning. A feed of low level moisture
being forced upslope ahead of the approaching shortwave will help
fuel the potential for downpours and locally heavy rainfall amounts
leading to the potential of flash flooding. QPF from the
operational models have maximum amounts of rainfall in the 2.5 to
3.8 inches...which tended to be supported by the SREF and GEFS
spaghetti plots and by machine learning first guess EROs. Felt a
Slight Risk area covers the potential for time being.

Bann

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