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FOUS30 KWBC 090930
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
530 AM EDT Wed Jul 9 2025

Day 1
Valid 12Z Wed Jul 09 2025 - 12Z Thu Jul 10 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE MID ATLANTIC...

...Mid-Atlantic and Southeast...

An anomalously moist and conditionally unstable air mass remains
entrenched across much of the eastern third of the CONUS, as a
pronounced mid-level trough extending from the Great Lakes to the
Mid-South gradually translates eastward. Height falls and DPVA from
this trough (along with increasing 0-6km bulk shear and enhanced
upper divergence from the favorable placement of a right-entrance
region of ~100 kt jet streak over New England) will coincide with
peak daytime heating and steep low-level lapse rates, eventually
resulting in widespread convective activity this afternoon across
much of the Mid-Atlantic (focused within the terrain and along the
leeward trough of the Appalachians) and into the Southeast (where a
TUTT cell is also playing a role, as some convection is already
ongoing early this morning in portions of southern GA and northern
FL). While much of the Southeast has been rather dry over the past
3-7 days, some portions of the Mid-Atlantic remain quite saturated
from prior days rainfall (and particularly from heavy rainfall in
association with Tropical Storm Chantal, which resulted in an area
of 4-10" of rainfall across central NC into south-central VA). A
Moderate risk was introduced with this forecast cycle for a
targeted portion VA (where flash flood warnings are even still in
effect at the time of writing from continuing convection
overnight), and this area represents the best overlap of
anticipated convective organization coinciding with vulnerable
antecedent conditions (as storms may be less organized farther
south where the bulk of rainfall occurred with Chantal, and
residence time may be too short farther north where stronger
dynamics will support the forward propagation of convection).

While the new Moderate risk area represents where more numerous
flash flood impacts are most likely to occur (with 00z HREF
neighborhood probabilities for FFG exceedance as high as 40-50%),
the Slight risk area has also been expanded fairly significantly to
encompass a large area from the Southeast (eastern GA into central
SC) into nearly all of the Mid-Atlantic (including the bulk of the
southern and central Appalachians) as PWs of 2.0"+ (near or above
the 90th percentile for much of the region) will allow for highly
efficient rainfall rates (with wet-bulb zero heights of 13-14k feet
allow warm rain processes to dominate) with localized totals of
1-3"/hr. Where these types of rates train/repeat, localized totals
of 2-5" are likely to occur (with the highest coverage of these
totals expected in and around the Moderate risk area). The threat
looks to be concentrated with peak daytime heating, mainly from
21-03z this afternoon and evening.


...Central Texas through the Southern Ohio Valley...

As the aforementioned mid-level trough crosses the OH Valley this
morning, a convective risk will be maintained for much of the day
from the Mid-South through the TN/OH Valley with elevated moisture
and increasing low-level lapse rates and instability from daytime
heating. Farther southwest into the Ark-La-Tex and central TX,
vorticity streamers from the trough are being shunted southwestward
(gradually rounding the persistent upper ridge over the Southwest)
and may help to locally organize convective activity. Elevated PWs
(generally between the 75th and 90th percentile) along with strong
daytime heating will result in generally scattered convection with
still efficient rainfall rates (up to 1-3"/hr) but limited coverage
and residence time resulting in isolated/localized totals of 2-4".
The Marginal risk was maintained and adjusted based on the new
guidance in this region.


...Central Plains into Mid-Mississippi Valley...

A shortwave rotating along the northern periphery of a ridge
centered over the Southwest U.S. will eject out of the northern
extent of the Front Range later today, leading to more focused
ascent and convective initiation portions of KS/NE into IA/MO by
later this afternoon/evening. While overall tropospheric moisture
and resulting rainfall rates are less impressive in this area,
there is some potential for upscale growth and convective
organization given increasing 0-6km bulk shear and steepening mid-
level lapse rates. While there is still considerable uncertainty
and hi-res model spread with the evolution and placement of higher
totals, HREF neighborhood probs suggest low-end chances (10-15%)
for localized 3" exceedance. This may bring a threat of isolated
flash flooding (which could go well into the overnight hours), and
the inherited Marginal risk area was adjusted accordingly based on
the new guidance.

Churchill


Day 2
Valid 12Z Thu Jul 10 2025 - 12Z Fri Jul 11 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
MID ATLANTIC...

...Tennessee Valley into the Mid-Atlantic and New England...

A warm and anomalously moist air mass looks to remain in place
across much of the Southeast and Eastern U.S. into Thursday
continuing a broad flash flood threat into yet another day.
Although upper-level forcing looks much less impressive overall
relative to Wednesday, still expect another round of primarily
diurnally driven convection focused along the terrain and
associated leeward trough of the Appalachians. Maintained an
inherited Slight risk area for more vulnerable portions of NC and
VA (from the Piedmont into the Coastal Plain) where the consensus
ensemble guidance signal remains highest for convective
organization (as vorticity streamers from the mid-level trough on
Wednesday may trail behind in the southern Appalachians long enough
to favorably support convective organization with peak daytime
heating on Thursday).


...Northern and Central Plains into the Upper Midwest...

By Thursday the persistent ridge aloft over the Southwest U.S.
begins to break down, as an upper-low off the northern CA coast
opens up into a shortwave trough on Wednesday and ejects eastward
ahead of a digging longwave trough over western Canada. These two
features look to interact over the Northern and Central Plains, but
there are still substantial differences between models in how
these features evolve and interact. PWs of 1.5"+ are expected
(near the 90th percentile for the region) with ample instability
and dynamics for organized convection and subsequent high rainfall
rates (as this shortwave trough looks much more potent relative to
the expected shortwave on Day 1). Maintained an inherited Slight
risk area that was adjusted based on the new consensus guidance.

Churchill


Day 3
Valid 12Z Fri Jul 11 2025 - 12Z Sat Jul 12 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE MID-ATLANTIC INTO THE SOUTHEAST, THE MID-MISSISSIPPI VALLEY
INTO THE MIDWEST, AND MUCH OF THE ROCKIES INTO THE CENTRAL AND
SOUTHERN HIGH PLAINS...

...Mid-Atlantic and Southeast...

As mid-level troughing becomes more established in the Northern
Plains into Day 3, ridging builds in response downstream and may
finally begin to suppress convection more significantly across the
northern Mid-Atlantic into the Northeast. While there are no clear
signs of significant convective organization at this juncture into
the Southeast and southern Mid-Atlantic, convective initiation with
scattered convection and locally high rainfall rates appears likely
(where ridging will be insufficient to fully suppress convection).


...Mid-Mississippi Valley into the Midwest...

More substantial convective organization is possible downstream of
shortwave troughs progressing/interacting in the Northern Plains
(placing the best risk more firmly into the Mid-MS Valley and Upper
Midwest). While the global ensemble guidance is coming into better
agreement with the QPF maxima, confidence is too low to introduce
a Slight risk with this cycle (with consensus guidance suggesting
1-3" totals, though so solutions suggest localized totals of up to
3-6" with inconsistent placement of the axis). Will continue to
evaluate with future cycles for the potential for an upgrade to
Slight risk.


...Rockies into the Central and Southern High Plains...

As the Southwest ridge continues to break down for a second day,
the global guidance signal for more substantial convective
initiation within the terrain of the Rockies increases into Friday
(and particularly so farther north into the northern/central
Rockies of WY/CO). Localized 1-2" totals (as indicated by both
downscaled deterministic GFS/ECMWF solutions and ensemble 1"
exceedance probabilities) in the sensitive terrain may lead to
localized flash flooding concerns, and more substantial convective
organization in association with shortwaves/vorticity maxima
rounding the ridge and coming off the terrain may allow for more
organized convection into the evening/overnight in the Central and
Southern High Plains.

Churchill


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