Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1101 AM EST Mon Dec 1 2025

Day 1
Valid 16Z Mon Dec 01 2025 - 12Z Tue Dec 02 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE GULF COAST AND DEEP SOUTH...

...16Z Update...
The Marginal Risk across portions of the Gulf Coast and Deep South
remains unchanged from the overnight cycle. 12Z HREF and and 6Z REFS
guidance are in good alignment depicting an uptick in shower and
thunderstorm coverage today along the northern flank of a
stationary front and surface wave. Low probabilities of rainfall
rates exceeding 1"/hr suggest the excessive rainfall threat today
should remain isolated at best, although some issues can't be
ruled out in sensitive urban areas.

Asherman

...Previous Discussion...
Very few changes were needed to the Marginal Risk area that
stretches from the Upper Texas Coast north and east along the Gulf
coast and into central Alabama and Georgia. A progressive shortwave
trough will round the southern periphery of an expansive upper
level low centered north of Hudson Bay, well into Canada. The
shortwave trough and associated 120-150 kt upper level zonal jet
will provide the forcing to allow storms to strengthen as southerly
flow off the Gulf provides ample moisture for the storms. The
limiting factor for heavy rainfall will be a lack of
instability...and while values could reach into the 500-1,000 J/kg
range, this along with the fast movement of the storms should keep
the flooding potential low along the Gulf Coast and Deep South. The
moisture moving in off the Gulf will be somewhat anomalous for
early December, with PWATs exceeding 1.75 inches along the coast,
or about 2 sigma above normal. A sweeping cold front will allow for
some organization to the storms. With heavy rain in portions of
Southeast Texas over the past 24 hours, locally saturated soils
could favor isolated instances of flash flooding in and around the
Houston area.

Further east, soils are much drier due to a distinct lack of
rainfall...however, this area will have more time before the cold
front sweeps through for storms to train over the same areas. This
is most likely to occur in a corridor from around Pensacola, FL
northeast to south of Atlanta. This area has very high FFGs, so
even here the threat for flash flooding will be low, as a similar
lack of instability should both hold storm intensity in check, and
at least at first the rainfall will be very beneficial by soaking
a parched landscape.

Wegman

Day 2
Valid 12Z Tue Dec 02 2025 - 12Z Wed Dec 03 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman

Day 3
Valid 12Z Wed Dec 03 2025 - 12Z Thu Dec 04 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

The very beginning of a multi-day rainfall event will begin to
unfold Wednesday night along portions of the Upper Texas and
Louisiana Gulf Coasts. For the most part, the guidance for this
time frame suggests most of the heaviest rainfall from
thunderstorms will remain offshore. However, at least some of that
rain could make its way inland. The threat remains sub-Marginal,
but the area will continue to be evaluated for a later introduction
of a Marginal Risk with future updates.

Wegman


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt