AWUS01 KWNH 092159
FFGMPD
FLZ000-ALZ000-MSZ000-LAZ000-100257-

Mesoscale Precipitation Discussion 1169
NWS Weather Prediction Center College Park MD
458 PM EST Mon Dec 09 2024

Areas affected...Parts of Southeast LA, Southern MS, and Southwest
AL

Concerning...Heavy rainfall...Flash flooding possible

Valid 092157Z - 100257Z

SUMMARY... A weakening line of showers and storms as well as
reforming convection upstream over south-central LA may lead to
additional chances for localized flash flooding this evening along
sections of the central Gulf Coast.

DISCUSSION... Same shortwave responsible for the breakout of
morning convection across southern LA is now crossing the central
Gulf Coast and entering the Southeast, while strong uniform
southwesterly flow continues to advect tropical moisture from the
eastern Pacific per GOES-West ADV LPW. PWs remain in the 1.6-1.9"
range per SPC's mesoanalysis and around the 90th climatological
percentile. These elevated PW values continue to advect further
eastward and across AL, but with instability remaining mostly
meager. SBCAPE values have climbed to above 1000 J/kg across
south-central LA mainly due to diurnal heating, which will wane in
the next few hours. However, speed maxes noted in GOES-East ML WV
exiting northern Mexico within the deep tropical moisture stream
imply convection may continue to linger a few hours past sunset.

This combination of elevated moisture, strong uniform
southwesterly flow, and remaining instability pool will lead to
additional chances for localized training thunderstorms capable of
containing hourly rainfall rates up to 2"/hr through around 9 pm
CT. A corridor of 3-5" of rainfall has already fallen per MRMS in
a SW-NE oriented line along the northern shores of Lake
Pontchartrain and southwestward. Otherwise, additional localized
corridors of 1-1.5" have already occurred. Therefore, even though
3-hr FFG remains widely above 2.5" there could be localized areas
more susceptible to flash flooding with 2-3" additional totals.
Urban locations will be most at risk within the broader isolated
flash flooding threat stretching from southern LA to southern MS.

Farther east into southern AL, a continuous band of rainfall
containing hourly rates around 1" is expected to continue within a
corridor of enhanced atmospheric moisture and very low
instability. This region may see more widespread rainfall amounts
above 1.5", but falling at lower rates. Any flash flood risk for
AL is considered low, with urban and poor drainage locations most
at risk for isolated impacts.

Snell

...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!_5mD1sgdjdxSJQUq--ZU_lFvtM-hwSmOEBRUzFgHv9etbNUToQBgD0D22VOt_sV5YVQq=
_eYBHEVqLVb4zGcYLULQXZA$  for graphic product...

ATTN...WFO...JAN...LCH...LIX...MOB...

ATTN...RFC...LMRFC...SERFC...NWC...

LAT...LON   31828764 31668652 30968662 30388839 29879017=20
            29609171 29979218 30519198 31059089 31578904=20
=20=20=20=20=20=20=20=20=20=20=20=20

=3D =3D =3D
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