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 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt