Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
857 PM EDT Wed Jul 16 2025
Day 1
Valid 01Z Thu Jul 17 2025 - 12Z Thu Jul 17 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE MID-ATLANTIC STATES, THE CENTRAL PLAINS, AND THE UPPER
MIDWEST...

...Central High Plains through the Great Lakes...
0100 UTC Update...Continue to remove the western edges of the
Slight and Marginal Risk areas across the Upper Midwest, while have
also made some tweaks to the Slight (removing SE Lower MI) based on
the latest observational and mesoanalysis trends.

...Ohio Valley into the Mid-Atlantic...
0100 UTC Update...Minor adjustments were made to the Slight and
Marginal Risk areas, based on the latest observational and
mesoanalysis trends. 18Z HREF exceedance probabilities again
support the highest risk for any isolated/scattered areas of
excessive rainfall lingering through 04-05Z.

...Gulf Coast...
Invest 93L exiting the northern Florida peninsula this morning
will drift westward into the northern Gulf on Wednesday. The
accompanying mid-level inverted trough/tropical wave will be forced
due west as it remains south of an elongated ridge extending from
the Atlantic Ocean. There continues to be quite a bit of spread of
intensity of the accompanying surface reflection to this feature
(and NHC continues a 40% chance of development) but the track
guidance has converged moving just south of the coast through the
next few days. Regardless of the exact track and development of
this system, the accompanying tropical moisture plume (PWs 2.25 to
2.5 inches, as much as +3 sigma according to the GEFS) will spread
onshore to support showers and thunderstorms with heavy rainfall
rates of 2-3"/hr. There continues to be uncertainty into how far
north any of this moisture will spread due to subsidence/dry air
beneath the ridge to the north, but guidance has begun to focus a
relative maxima across southeast LA, and potentially as far east as
Mobile Bay, AL.

...Arizona and New Mexico...
2015Z Update...Based on the latest observational trends (visible
satellite and mosaic radar in particular), along with the latest
HREF and RRFS 1/3/6hr QPF exceedance probabilities...have expanded
the Marginal to include the Sacramento Mtns in NM. Another update
may be necessary to expand the Marginal north to capture the
convective clusters firing across portions of the Grand Canyon
Country in northern AZ.

Active convection is likely again today across the Southwest as
the mid-level ridge weakens and weak impulses, some of which are
convectively enhanced by thunderstorms from Tuesday, move across
the region. PWs are expected to continue to be above 1.25", highest
across southern AZ, but with a slow decrease in intensity and
coverage of this PW plume. Additionally, probabilities for CAPE
exceeding 500 J/kg are lower and confined east of the greatest
moisture today, indicating that coverage and intensity of
thunderstorms should be less than what occurred Tuesday. Despite
that, convection should still be relatively widespread, but
possibly displaced north of previous activity, although any weak
remnant MCVs could enhance local ascent leading to local flash
flood impacts, most likely should any thunderstorms with 0.5"/hr
rain rates track across burn scars or sensitive terrain.

Hurley/Weiss

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