Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1254 PM EDT Sat May 3 2025

Day 1
Valid 16Z Sat May 03 2025 - 12Z Sun May 04 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
EASTERN U.S. AND THE SACRAMENTO MOUNTAINS OF NEW MEXICO...

16Z Update...
An upper-level low is forming over the mid-Mississippi region and
becomes cutoff over Kentucky tonight as the jet focuses over
eastern Canada. Low level flow is drawing Gulf moisture through and
ahead of the system from the Gulf Coast up through the Eastern
Seaboard. Several focus areas for thunderstorms are expected
through tonight in the broad area which covered by a contiguous
Marginal Risk.

Ohio Valley to Gulf Coast...
Locally heavy activity has developed ahead of a surface low over
western TN with scattered storms south ahead of the advancing cold
front through MS and north along a stalled boundary that extends to
the upper Ohio Valley. This activity may pivot over eastern
KY/southern OH through the middle afternoon while activity over AL
to the Gulf Coast should be more progressive.

Carolinas, Central Appalachians and Mid-Atlantic...
Lee trough development over the Piedmont in the Carolinas later
this afternoon will allow potentially training activity in deep
SSWly flow there well into the evening, so the Marginal Risk was
expanded east a bit over SC/NC. This activity lifts north through
the central Appalachians into this evening with localized flash
flood threats. Later tonight the activity shifts east with some
training potential, so the Marginal was maintained east through the
Baltimore/Washington urban centers.


Northeast...
The northern end of the moisture plume converges on a frontal zone
over Upstate NY and central New England through this afternoon
bringing potential for excessive rain despite strong deep layer
flow. The Marginal Risk was expanded north into central New
England. A second round of development is expected farther south
this evening in the Hudson Valley and southern New England which
was already covered by a Marginal.


New Mexico...
Afternoon convection over the Sacramento Mtns brings a threat for
runoff issues from burn scars into this evening, so the Marginal
Risk is maintained.


Jackson

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


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