Mesoscale Precipitation Discussion 0005
NWS Weather Prediction Center College Park MD
455 AM EST Tue Jan 09 2024

Areas affected...portions of southeast and east-central
AL...west-central and northern GA...western SC/NC...far East TN

Concerning...Heavy rainfall...Flash flooding likely

Valid 091000Z - 091600Z

Summary...Numerous instances of flash flooding are likely across
portions of southern AL (along with the threat of locally
significant flash flooding) where 1-3"/hr rainfall rates will
continue (with additional short-term totals of 2-4"). Elsewhere,
localized flash flooding is considered to be possible with
rainfall rates mostly capped at 1"/hr (but still accumulating to
the 2-4" range).

Discussion...An MCC (mesoscale convective complex) continues to
propagate eastward across southern AL and the western FL Panhandle
early this morning. The strongest convection (and coldest cloud
tops via GOES IR imagery) are located just to the east of the
attendant low pressure system and cold front, effectively
propagating eastward along the gradually northeastward advancing
warm front. Repeating of 1-2"/hr rainfall rates has occurred most
efficiently along the warm front, as semi-discrete convective
cells are overtaken by a more dominant eastward moving squall
line. This has resulted in localized streaks of 3-6" over the past
6 or so hours, gradually coming to an end in southern MS.
Meanwhile, southern AL will continue to see some of the heaviest
rainfall over the next several hours in association with the
leading convection and approaching squall line, likely resulting
in additional accumulations of 2-4". This overlaps already
saturated soils with corresponding flash flood guidance of 1-3",
and additional numerous instances of flash flooding are most
likely across this region (with relatively good agreement amongst
the hi-res models, including the experimental WoFS, and well
supported by the observational trends). Locally significant flash
flooding also remains a threat where these 2-4" totals overlap
with prior totals of 2-5".

Farther northeast into west-central and northern GA and
surrounding portions of SC, NC, and TN, rainfall rates are more
likely to be capped at around 1"/hr due to the absence of
instability. Instead, rainfall will largely be more stratiform
resulting largely from mid and upper-level forcing (as well as
from jet stream transportation of the hydrometeors from the
primary MCC farther south). This may still result in some 3-hr
totals exceeding 2" or 6-hr totals exceeding 3" (per HREF 40-km
neighborhood probabilities ranging from 20-50%), but this is
relatively close to the corresponding flash flood guidance (and
antecedent conditions are relatively dry, per NASA SPoRT-LIS 0-1m
soil moisture around the 2nd or 3rd decile). Perhaps the most at
risk localities in this region are within the terrain surrounding
the GA/SC/NC border region, where upslope flow from the incredibly
strong low-level jet should contribute to the greatest chance of
locally exceeding 3" through 16z. Overall, flash flooding is
considered possible across this region through mid-morning, but
this may change by mid-day and early afternoon with continued
repeated ~1"/hr rates in the vicinity of western SC/NC.

Churchill

ATTN...WFO...BMX...CAE...FFC...GSP...HUN...MOB...MRX...TAE...

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

LAT...LON   36008294 35828264 35978197 35728133 35278132
            34578157 32898334 32148395 31228483 30578557
            30678629 30748690 30648781 30868838 31728804
            33378667 34558551 35118477 35458426 35958337