Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1100 AM EST Sat Nov 29 2025
Day 1
Valid 16Z Sat Nov 29 2025 - 12Z Sun Nov 30 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHEAST TEXAS...
...16Z Update...
Morning surface observations and 12z Brownsville RAOB depict the
return of a modified Gulf airmass ahead of a strong cold front
surging into the Southern Plains. As the front approaches Southeast
Texas, organized convection is expected to initiate this afternoon
in the vicinity of a pre-frontal trough and returning warm front.
12Z CAM guidance suggests some training potential with this
convection in the 0-6Z timeframe along these boundaries before the
front sweeps through. While much of the HREF guidance has trended
upward in the magnitude of the rainfall footprint tonight, the
modified airmass should limit hourly rainfall rates when combined
with 500-1000 J/kg MUCAPE. Thus, maintained the Marginal Risk with
an expansion along the I-10 corridor to account for urban heavy
rainfall concerns.
Asherman
A cold front moving south down the Plains will run into a plume of
Gulf moisture moving into eastern Texas tonight. The clash of these
two air masses is expected to result in some limited thunderstorm
development this evening across portions of east central Texas and
northern Louisiana. Overnight tonight, the line will press
southward. As the line encounters ever increasing amounts of Gulf
moisture, convective coverage is likely to also increase across
southeastern Texas. Since the plume will continue northeastward up
the front, additional convective development is also expected
across central Louisiana. However, both due to increased distance
from the Gulf and poor instability (values broadly have come down
to at most 500 J/kg of MUCAPE), the storms further north and east
into Louisiana are likely to remain as a progressive skinny line of
convection. Meanwhile, in the Marginal Risk area across southeast
Texas, closer proximity to the Gulf should allow for a bit of pre-
frontal convection to form before the more organized line of storms
moves through. Given the lack of instability, progressive movement
of the storms, time of day (overnight tonight), and very dry soils
present along the Gulf Coast, the thinking as regards coverage of
flooding remains the same... only very isolated flash flooding
possible where any prefrontal storms train over urban or other low-
lying, flood-sensitive areas. This remains a lower end (near 5%)
flood risk. For the most part, the rain expected tonight will be
beneficial. The line will move through the Houston metro around
midnight local time, then both weaken and move into the Gulf beyond
that.
Wegman
Day 2
Valid 12Z Sun Nov 30 2025 - 12Z Mon Dec 01 2025
The probability of rainfall exceeding flash flood guidance is less
than 5 percent.
Wegman
Day 3
Valid 12Z Mon Dec 01 2025 - 12Z Tue Dec 02 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
CENTRAL GULF COAST TO THE SOUTHERN APPALACHIANS...
A fast-moving progressive shortwave trough that extends from an
expansive upper level low over Canada will provide the upper level
forcing for cyclogenesis along a potent cold front that will
roughly parallel the Gulf Coast and Eastern Seaboard. The low will
begin to form along the Texas Gulf coast during the day Monday,
then track ENE across the Deep South, ending the period near the
South Carolina/Georgia border. As the low tracks along the Gulf
Coast, it will continually add Gulf moisture to its circulation,
while also thriving on the baroclinicity brought on by a
reinforcing cold air mass moving southeast from the Midwest. PWATs
in the warm, moist Gulf air mass will exceed 1.75 inches in some
areas. However, any instability will likely remain along the
immediate coast, with very little instability inland. This supports
an overrunning rainfall scenario, rather than an overly convective
one. A prolonged period of light to moderate rain is expected
across much of the South as a result. The heaviest rain is forecast
from near New Orleans northeast to the southern Appalachians. It's
in this corridor that the highest probability of flash flooding
exists. The qualifier to this statement however is that FFGs across
the Deep South are quite high as a result of recent dry weather
and therefore very dry soils. This will favor most of the rainfall
associated with this low being beneficial to affected areas.
Isolated flash flooding is most likely in urban or flood-prone
areas, as well as in the flashier streams that drain the Southern
Appalachians.
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