Mesoscale Precipitation Discussion 1256
NWS Weather Prediction Center College Park MD
734 PM EST Mon Dec 01 2025

Areas affected...portions of the central Gulf Coast

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

Valid 020034Z - 020634Z

Summary...A combination of cell training and backbuilding should
continue to lead to hourly rain amounts to 1.75" with local totals
to 4", which could cause flash flooding in urban areas.

Discussion...Instability across portions of the central Gulf Coast
continues to rise ahead of a negatively-tilted shortwave across
OK.  Precipitable water values are ~1.6" per GPS data and MU CAPE
values of 500+ J/kg lie across the southeast tip of LA and
continue shifting north towards the MS/AL barrier islands.  Radar
estimates from LIX/Hammond LA indicate that hourly amounts peaked
near 1.75" not far from the eastern suburbs of New Orleans
recently, with local totals above 2.5" so far.  Occasional hourly
rain amounts to 1.5" have been seen in backbuilding convection in
southernmost AL.  Effective bulk shear of 25-45 kts lurks across
the area which is helping to form a band within an area of 850 hPa
confluence.

The band is showing some signs of shifting northward across
southern AL and slightly eastward in southeast LA.  Additional
activity south of the LA/MS coasts within a convergence zone which
extends from northwest Cuba towards the central Gulf Coast could
advect northward towards portions of this area in the next several
hours and cause additional issues.  The guidance has not been
ideal in this region thus far -- too far north and too light --
though the 18z hi-res NAM appears to have the best idea, so used
it as a starting point for the MPD bounds, making some adjustments
based on radar reflectivity trends.  The region has been dry, so
flash flood guidance values are high.  Hourly amounts to 1.75" and
local totals to 4" appear possible where cells train and/or
backbuild, which would be most problematic in urban areas.

Roth

ATTN...WFO...BMX...LIX...MOB...TAE...

ATTN...RFC...ALR...ORN...NWC...

LAT...LON   31928616 31298582 30558670 30248743 30078846
            29938870 29778905 29439024 29689078 30768934
            31778728