611
AWUS01 KWNH 180634
FFGMPD
FLZ000-GAZ000-ALZ000-MSZ000-LAZ000-181230-

Mesoscale Precipitation Discussion 0286
NWS Weather Prediction Center College Park MD
234 AM EDT Sat May 18 2024

Areas affected...Southern LA...Southern MS... Southern
AL...Southwest GA...Western FL Panhandle...

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

Valid 180635Z - 181230Z

SUMMARY...Efficient tropical rain showers with rates over 2"/hr
possible crossing wet soil conditions from recent heavy rains.
Fast eastward propagation may limit very high totals, but
scattered incidents of flash flooding becoming possible through
daybreak.

DISCUSSION...06z surface analysis depicts a weak/subtle wave in
proximity to the Pearl River in S MS with a rain-cooled reinforced
front extending across SE LA into the Northwest Gulf.  A
stationary front extends eastward across S AL into S GA; both
defined by the 7-10 degree Td differences from upper 60s/low 70s
north relative to the upper 70s to isolated 80s from a very warm
northern Gulf of Mexico.  Additionally, southeast of the front
especially in the warm sector south of the surface wave, there
remains some temperature/dewpoint spread with temps in the low 80s
and higher instability with weakly capped MLCAPEs of 3000 J/kg
along and just west of the deeper overall moisture axis that goes
from the western Gulf to near Mobile Bay with total PWAT values at
or above 2" before pooling along the stationary front further east
into GA.

Aloft, WV suite denotes a dry slot across SE TX nosing into
central LA generally along the DPVA on the southeast periphery of
the elongated/positive tilt shortwave trough over E TX into AR.
Sufficient shortwave ridging in the subtropical jet across the
Western Gulf becomes diffluent downstream into the area of concern
through S MS/AL providing a favorable environment for tropical
showers/thunderstorms to develop over the next few hours.  Deep
layer flow is fairly unidirectional from WSW to SW across LA to AL
before splitting more downstream into GA, so there will be favored
embedded cell motions that may support repeating/training as
convection becomes more abundant with time. However, stronger
eastward progression/propagation is expected and may limit
duration at any given spot but localized interaction/frictional
convergence in proximity to the Gulf across SE LA into S MS/S AL
and western FL panhandle may allow for increased duration to
support the greatest totals which may reach 3-4" though 12z.

Otherwise, quick hitting 2-3" totals are possible as the cell
expand/mature into S AL.  Here, there is some concern that cells
will start to cross the most saturated soils where FFG has not
rebound and are below the 1.5"/hr and >2"/3hr values, making the
potential for flash flooding more likely, though there is some
greater uncertainty to the efficiency and coverage of convection
being furhter from the Gulf and north of the frontal zone.

South-central LA...
Uncertainty is very high for potential for stronger thunderstorms
to maintain.  As mentioned, the front was reinforeced by
rain-cooled, stable air over central LA into SW MS.  Over-running
thunderstorms are becoming more prolific across the NW Gulf
approaching the SW LA coast; but given distance from the deep
moisture/unstable air, maintaining stronger updrafts is very
uncertain.  However, the area has also seen prolific rainfall
north of I-10/12 across the area and so rates of up to 2"/hr and
spots of 2-3" may present a concern as well and so the area is
included in this MPD though less confident than areas of SE LA
into S MS/S AL.

Gallina

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...BMX...FFC...JAN...LCH...LIX...MOB...TAE...

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

LAT...LON   32708500 32408377 31598328 30788408 30258618
            30018739 29458837 28918971 29149131 29409271
            29779333 30409234 31658910 32478690