Mesoscale Precipitation Discussion 0709
NWS Weather Prediction Center College Park MD
225 PM EDT Tue Jul 23 2024
Areas affected...northern/central Alabama, northern Georgia,
southeastern Tennessee
Concerning...Heavy rainfall...Flash flooding possible
Valid 231824Z - 240024Z
Summary...Scattered showers and thunderstorms are migrating
east-northeastward across the discussion area while producing
spots of 1 inch/hr rain rates. The repeating nature of these
downpours and cell mergers may prompt isolated instances of flash
flooding through 00Z - especially across urbanized/sensitive areas.
Discussion...Deep convection was embedded in west-southwesterly
flow aloft across the discussion area, with a mix of cells and
clusters noted per radar mosaic imagery. Despite appreciable
forward movement (at around 20 knots), cells were oriented
favorably for repeating and a few spots of 1 inch/hr rain rates
were beginning to emerge south of Huntsville over the past half
hour or so. Additional cells were developing upstream in
northeastern Mississippi. The overall pattern suggests potential
for some locales to experience multiple rounds of heavy rainfall,
with totals exceeding 2.5 inches in spots through 00Z. These
rates will occur in areas containing 1.5-2.5 inch/hr FFG
thresholds (locally lower in Birmingham Metro and portions the
southern Appalachians/northern Georgia). Weak low-level shear
will foster areas of congealing as cells/clusters through the
afternoon, with mergers and local training potentially resulting
in spots of 2 inch/hr rain rates. This is also supported by the
abundantly moist/unstable environment (2+ inch PW values, 1500
J/kg MLCAPE) supporting ongoing storms.
The overall scenario is likely to continue through 00Z and
potentially just beyond sunset. Areas of 1-2 inch/hr rain rates
are expected to remain likely during that time. Additional
convection from central Mississippi/southern Alabama will also
merge with ongoing storms later in the afternoon (per 12Z HREF
guidance), continuing flash flood potential especially across
southwestern portions of the discussion area. The storms (and
attendant flash flood threat) should be primarily diurnally
driven, with a decrease in overall risk expected at some point
after sunset.
Cook
ATTN...WFO...BMX...FFC...GSP...HUN...JAN...MEG...MRX...OHX...
ATTN...RFC...LMRFC...OHRFC...SERFC...NWC...
LAT...LON 35638375 34938294 34338281 33918310 33398385
32698527 32698688 32778802 33548841 34818807
35238658 35588502
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