From Mike Powell@618:250/1 to All on Friday, September 13, 2024 08:22:00
AWUS01 KWNH 131006
FFGMPD
GAZ000-ALZ000-131530-
Mesoscale Precipitation Discussion 1001
NWS Weather Prediction Center College Park MD
606 AM EDT Fri Sep 13 2024
Areas affected...Portions of Eastern AL...Western GA
Concerning...Heavy rainfall...Flash flooding possible
Valid 131005Z - 131530Z
SUMMARY...Broken areas of heavy showers and thunderstorms may
support an isolated threat of flash flooding this morning.
DISCUSSION...The latest GOES-E WV satellite imagery in conjunction
with dual-pol radar shows a broken cluster of heavy showers and
thunderstorms lifting northeastward up across portions of eastern
AL which will likely spread into areas of western GA early this
morning. The convection which is relatively warm-topped in nature
is being driven by a modest shortwave ejecting across southeast AL
while interacting with a generally north-northwest to
south-southeast axis of moisture convergence and modest
instability near a quasi-stationary front.
Broad and moist, confluent low-level flow is noted across much of
the central Gulf Coast region as Post-Tropical Cyclone Francine
continues to move slowly across areas of eastern AR and bumps up
against surface high pressure nosing well south into the interior
of the Southeast. The instability axis is characterized by MUCAPE
values of 500 to 1000 J/kg across central and southern AL over
into portions of west-central GA.
Quite a bit of mid to upper-level dry air is showing up in the WV
satellite imagery along with CIRA-ALPW data in the 500/300 mb
layer which is helping to limit/cap the vertical extent of
convective development, but there is sufficient forcing and
moisture noted below 500 mb to favor relatively efficient and
warm-topped convection with rainfall rates of 1 to 2 inches/hour.
The overnight HREF guidance and recent HRRR runs have a poor
handling of the ongoing activity, but satellite trends suggest
some increasing trends toward heavier rainfall rates with some
cloud-top cooling. This suggests a corridor of stronger forcing
which is also aligned with the aforementioned moisture convergence
and instability axis.
Some occasional backbuilding of the broken complex of convection
will be possible this morning which may allow for sufficient
persistence of heavier rainfall rates to support some spotty
totals of 2 to 4+ inches. This may result in an isolated threat of
flash flooding which would likely be primarily a threat to the
more sensitive urban environments.