Mesoscale Precipitation Discussion 1032
NWS Weather Prediction Center College Park MD
1258 PM EST Sat Dec 01 2018

Areas affected...Western FL Panhandle...Southern Alabama

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

Valid 011757Z - 012357Z

Summary...Hourly totals up to 2" will be possible as a line of
slow moving convection drifts onshore across the western FL
panhandle and southern Alabama. Through 23z / 5 PM CDT, 3-5" will
be possible which could result in localized flash flooding.

Discussion...Recent surface analysis shows a warm front across the
far northern Gulf of Mexico with a slow advancement northward
toward the coastline. Aloft, southwesterly flow exists with broad
forcing for ascent, loosely within a right entrance region of a
jet max over the Arklatex region. Anomalously high moisture exists
across the Gulf Coast region with recent mesoanalysis showing
PWATs of 1.8 to near 2.0", which is roughly 2-2.5 SD above the
mean. SBCAPE exceeding 500 J/kg is just beginning to move onshore
per recent RAP analysis while MUCAPE upwards of 1500 J/kg exists
already across the region.

Recent radar returns from KLTH, KEVX, and KMOB show hourly rates
exceeding 1.5" associated with the ongoing convection offshore. As
this activity moves onshore coincident with the increase in
SBCAPE, hourly rates up to 2" will be possible across southern
Alabama and the western FL panhandle this afternoon. In general,
the hi-res guidance has not performed well with this activity
since this morning and has generally be too far north/fast with
the convection forming near the warm front. Though, it is expected
that this convection will make it onshore early this afternoon and
slowly drift east/northeast across the FL panhandle and adjacent
southern Alabama. With the mean flow parallel to storm motion and
favorable 850 mb moisture transport, there is concern for
training/backbuilding across the area.

Antecedent conditions and FFG are less conducive for flash
flooding, with 1-hr guidance of 3-4". However, earlier scattered,
less intense showers/thunderstorms produced amounts of 1 to
locally 1.5" across the area per mesonet observations, which may
help to lower these values in the near term.

As a result, with the threat of localized 3-5" amounts with
periods of intense rainfall rates up to 2"/hr, flash flooding will
be possible, especially across urban areas or poor drainage
locations, through this afternoon.

Taylor

ATTN...WFO...MOB...TAE...

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

LAT...LON   31308662 30878529 30528489 30048488 29758535
            30298651 30078808 30838806 31098756