Mesoscale Precipitation Discussion 1156
NWS Weather Prediction Center College Park MD
955 PM EST Wed Nov 13 2024

Areas affected...Eastern MS...Much of AL...Far Western FL
Panhandle...

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

Valid 140255Z - 140830Z

SUMMARY...Intense thunderstorms capable of a quick sub-hourly 1-2"
near the front pose mainly urban flash flooding threat, while
slower moving more scattered supercells within the Coastal Plain
may result in a axis or two of 3-4" totals with similar localized
flash flooding concerns through early overnight period. 

DISCUSSION...GOES-E WV suite depict slightly below average closed
low crossing IA/MO with a well defined cold front/warm conveyor
belt system across the Lower Ohio, Western Tennessee River Valleys
extending south into MS where it is interacting with enhanced deep
layer moisture and remnant low level circulation energy of ex-TC
Rafael.  CIRA LPW and RAP analysis denote enhanced tropical
moisture and higher than normal theta-E air extending northward
along a core of 30-35kt 850 southerly low-level jet.  However, the
deepest moisture and unstable air remains further south, generally
in the lower 2/3rds of eastern MS into western AL, with maximum
unstable air of 2000-2500 J/kg along the central Gulf Coast. 
Strong height-falls and right entrance ascent to 3H 100 kt Jet in
the central MS Valley is providing the oblique but sufficient
intersection with the cold front to generate convective cells from
Starkville/Columbus MS southward to the tail of the
front/inflection near the apex of the remnants of Rafael east of
McComb.  Given the stronger LLJ/divergence aloft remains displaced
from best moisture/instability, cells still remain potent with
capability of generating 1-1.5" total though with waning
instability, updrafts continue to diminish from north to south
over the next few hours.  Still, there are urban targets along
this track and with the sub-hourly totals near or over 1hr FFG
particularly north and west AL and west central MS remains at low
end risk for localized flash flooding for the next few hours.

Further south, slightly backed flow as a result of the sheared
inflection from ex-Rafael, moisture/instability axis is extended a
tad eastward.  Effective bulk shear is stronger to the north but
given stronger SBCAPEs and backed low level flow, the potential
for widely scattered supercells remains possible.  Slower eastward
propagation combined with natural slowing of rotating cells,
allows for increased duration.  Combined with broader updraft and
enhanced directional convergence at the base of the updrafts,
greater moisture flux of higher surface to 850mb moisture
(gnerally 1.5"-1.75 per CIRA LPW through 700mb) will increase
rainfall efficiency and localized duration.  Rates of 2-2.5"/hr
with localized spot of 3"+ possible in 1-2 hours pose a flash
flood risk, especially given recent above average rainfall per
AHPS and lowered FFG values in S AL.   However, currently the best
candidate cells is along/just south of Mobile Bay and in Greene
county MS moving into Washington AL.   As such, flash flooding
remains possible through the early overnight period as well across
S AL into far W FL panhandle.  

Gallina

ATTN...WFO...BMX...HUN...JAN...MOB...

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

LAT...LON   34268695 34178620 33838592 33308574 32408606
            31518649 30568702 30258757 30218794 30368823
            30738837 31038898 31348964 32108965 33258859
            33948776