FOUS30 KWBC 281946
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
346 PM EDT Mon Jul 28 2025

Day 3
Valid 12Z Wed Jul 30 2025 - 12Z Thu Jul 31 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE MIDDLE MISSISSIPPI VALLEY AND FOR PORTIONS OF THE FRONT RANGE
AND ADJACENT HIGH PLAINS...

...Mid MS Valley...

21Z update... The area highlighted for the Slight Risk area remains
in good order, only minor reshaping of the boundary made to reflect
the latest WPC QPF and model trends.

Campbell

At 12z Wednesday it seems likely that we will have some degree of
organized convection ongoing in the vicinity of IA, although at
this lead time getting these specifics right is tricky.
Nonetheless, it appears probable that a better defined
shortwave/MCV will be associated with this convection and slowly
move east across IA/MO/IL and vicinity Wednesday into Wednesday
night. Meanwhile we will have a slowly southward shifting cold
front helping focus convergence, and the right entrance region of
the upper jet adding some divergence aloft. With plentiful CAPE
near the front and PWs locally over 2", the ingredients for areas
of excessive rainfall are in place. Some uncertainty remains on the details...but 00z models are coming into a better consensus on the
favored axis for heavy rainfall..generally stretching across
portions of IA, northern MO and into central/northern IL and
possibly portions of IN.

...Southwest and High Plains...

21Z update... There is a growing signal for convection to fire up
along the Front Range and the adjacent high plains. The nature of
coverage still seems to be scattered however guidance has
consensus of 1 to 2 inches for areal maximums with isolated
locations potentially reaching 3 inches or higher. In coordination
with the local forecast offices, opted to raise a Slight Risk for
eastern Colorado, southeast Wyoming, western Kansas, small portions
of the Oklahoma and Texas Panhandles, and northeast New Mexico.

Campbell

Isolated to scattered convection will likely develop near areas of
terrain from NM into the Rockies. Generally not looking like the
greatest forcing, so the degree of convective organization remains
unclear. At the moment most models indicate mostly
isolated/scattered development, and generally not enough coverage
for anything more than a Marginal risk. However there is some
potential for a few organized clusters to move off the terrain
into the High Plains, and so can not rule a targeted Slight risk or
two as we get closer in time and have more high res guidance to
interrogate.

...Elsewhere...

A broad Marginal risk extends from the central Gulf Coast all the
way into portions of New England. High PWs and CAPE and convective
coverage will drive the risk from the Gulf Coast into the TN
valley. A lack of organization may keep FFG exceedance coverage
down, but high rainfall rates will likely locally approach or
exceed FFG. A cold front will drive the risk form portions of the
OH valley into New England. Generally quick cell motions and the
lack of a significant QPF footprint in the 00z models keep this
risk at a Marginal level.

Chenard
$$
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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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