Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
225 PM EST Tue Nov 25 2025

Day 1
Valid 16Z Tue Nov 25 2025 - 12Z Wed Nov 26 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHEAST AND SOUTHERN APPALACHIANS, SOUTH TEXAS, AND ALSO FOR
THE COASTAL PACIFIC NORTHWEST...

...16Z Outlook Update...
The ongoing forecast is generally on track with only minimal
changes needed based on latest short-term convective evolution.
Reference Mesoscale Precipitation Discussion #1250 for short-term
flash flood risk evolution across Alabama and vicinity.

Later today, convection will increase in coverage and intensity
across eastern Mississippi and migrate quickly eastward across
Alabama into Georgia and southeastern Tennessee through the
overnight hours. CAMs depict a mix of cellular and linear
convective models with little opportunity for convective training
that would enhance local flash flood risk. Marginal Risk and
attendant probabilities remain appropriate for today's flash flood
threat, with urban areas, sensitive/low-lying areas, and areas that
have wet soils from prior rainfall (i.e., western/northern Alabama)
experiencing a locally higher (but still isolated) threat of
excessive runoff.

A small Marginal Risk area was drawn for Deep South Texas primarily
for the overnight (03Z-12Z) period. A stalling front should drift
toward that area during that timeframe. Meanwhile, weak mid-level
waves should initiate convection along and south of the front where
moderate instability and very moist thermodynamics reside (PW
values ~ 1.75 inch). While sufficient steering flow aloft exist for
appreciable cell movement, any localized backbuilding near the
front could prompt local 3 inch rainfall amounts that could cause
excessive runoff especially near urban/sensitive locales.

The remainder of the forecast (with Marginal Risk/probabilities for
excessive runoff across the Pacific Northwest) is on track.

See the prior forecast below for more information.

Cook

...Previous Discussion...

...Southeast states...

The storm system crossing the southern tier states will continue
to have a plume of Gulf moisture surging north ahead of the cold
front through Tuesday afternoon, mainly from southeastern
Mississippi to the southern Appalachians. The magnitude of the
rainfall and also the coverage is expected to wane compared to
yesterday as the storm system becomes more elongated and
progressive. Recent CAM guidance has swaths of QPF maxima on the
order of 1.5 to 3 inches from central Alabama to eastern Tennessee
and western North Carolina, with the RRFS taking some of the
heavier rains as far north as the Kentucky state line. Only small
changes were necessary to the inherited Marginal Risk area, with a
modest extension northward to include more of the southern
Appalachians, and a little farther westward to areas closer to the
Mississippi border.

...Pacific Northwest...

A marginal atmospheric river event will affect the coastal ranges
and the Cascades from central Oregon northward through Tuesday
night, followed by lighter precipitation going into Wednesday.
There will not be much instability to work with, so this will tend
to keep rainfall rates in check, but the duration of moderate
rainfall with rates near 0.25 inches per hour leading to areas of
1-2 inch daily rainfall totals may just be enough to lead to some
localized instances of minor flooding from the northern coastal
ranges of Oregon to the Olympic Peninsula. The timing for this has
also sped up some, to the point where the majority of the rainfall
is now expected in the Day 1 period instead of the Day 2 period,
so no areas are necessary at this time beyond 12Z Wednesday for
this region.

Hamrick


Day 2
Valid 12Z Wed Nov 26 2025 - 12Z Thu Nov 27 2025

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

Chenard


Day 3
Valid 12Z Thu Nov 27 2025 - 12Z Fri Nov 28 2025

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

Chenard


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