FOUS30 KWBC 290814
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
414 AM EDT Tue Jul 29 2025

Day 3
Valid 12Z Thu Jul 31 2025 - 12Z Fri Aug 01 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE MID-ATLANTIC INTO SOUTHERN NEW ENGLAND...

...Mid-Atlantic into New England...
Heavy rainfall and at least some flash flooding appears likely
Thursday across portions of the Mid-atlantic and possibly into
southern New England. Convection is likely to focus along a slow
moving cold front, with broad mid level troughing and height falls
providing large scale ascent. The upper level jet is displaced
pretty far north, however still likely to get some enhanced upper
level divergence into the Mid-Atlantic from this feature. 

There is quite a bit of model spread with the details of this 
convective risk. The driver of most of this spread appears to be a
shortwave/MCV that intensifies associated with the NE/IA 
convection Tuesday night into Wednesday. This feature then tracks 
eastward and enhances lift over the Mid-Atlantic and Northeast. 
Some models have a stronger more well defined feature, which then 
helps keep the front a bit farther north resulting in a farther 
north QPF axis. At the moment it does seem like the 00z NAM and 12z
ECMWF are a bit too amplified with this feature...thus find it 
unlikely that the heaviest QPF swath will be as far north as they 
depict. The 00z ECMWF came south a bit, but probably still too far
north. Both the 00z ECMWF AIFS and 18z NOAA EAGLE machine learning
ensembles show highest probabilities closer to the I95 corridor, 
generally from DC to PHL to NYC and into southern New England. This
also seems to fit the expected placement of higher instability/PW 
overlap. Also will note that the 00z RRFS has a very similar axis 
as well. Thus the Slight risk will remain positioned across this 
corridor, although confidence on this exact placement remains 
average at best given some of the run to run differences we are seeing.

Wherever the event does focus there is certainly a potential for 
higher end impacts. PWs near the slow moving front will be over 2"
over a broad area, with embedded values likely getting towards 
2.3". We should also have plenty of instability to work with, which
combined with the high PWs, should drive heavy rainfall rates. 
Combine that with some training potential near the slow moving 
front, and can not rule out the possibility of eventually needing a
Moderate risk...especially if the more sensitive Urban corridor 
remains a focus going forward.

...Gulf Coast into OH Valley...
Another day of slow moving pulse thunderstorms is expected over a
large swath of the region. Similar to Wednesday, high PWs and CAPE
and convective coverage will drive a localized flash flood risk. A
lack of organization may keep FFG exceedance coverage down, but 
high rainfall rates will likely locally approach or exceed FFG.

...Rockies into the Plains...
Scattered convection is likely from eastern AZ into NM northward
all the way into MT. Currently not seeing a strong indication of
organization that would lead to Slight risk level flash flood
coverage. However localized flash flooding will again be possible
over this broad region. There are some height falls beginning to
approach from the west, so that could perhaps end up driving a 
more organized risk somewhere within this broad Marginal risk. But
at the moment not enough confidence to go with any Slight risk 
areas for this region.

Chenard
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