Subj : MESO: Heavy rain - floodi
To   : All
From : Mike Powell
Date : Thu Apr 27 2023 17:29:00

AWUS01 KWNH 272144
FFGMPD
SCZ000-FLZ000-GAZ000-280343-

Mesoscale Precipitation Discussion 0213
NWS Weather Prediction Center College Park MD
544 PM EDT Thu Apr 27 2023

Areas affected...Southeast GA...Extreme Southwest SC...Northeast
FL

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

Valid 272143Z - 280343Z

Summary...Convective clusters are expanding across portions of
Georgia and Northern Florida ahead of an eastward propagating MCS.
Rainfall totals upwards of 5" through this evening could support
isolated flash flooding, especially atop urbanized areas.

Discussion...Recent radar and IR imagery trends highlight
expanding and intensifying thunderstorm clusters across Southeast
Georgia and Northeast Florida ahead of a mature MCS crossing the
Panhandle. Confluent, southwesterly low-level inflow at 850 mb
ascending a sea breeze/effective front was helping to drive this
cluster activity, with strongly diffluent flow aloft noted to
support updraft maintenance and intensity.

Observations and objective analysis estimates depict a favorable
environment for organized convection capable of 2-2.5"/hour rates.
1500-3000 J/kg MUCAPE was noted ahead of the MCS according to SPC
mesoanalysis, with 1.5-1.6" PWATs nosing into the Georgia Coastal
Plain per GPS (which would be above the 90th percentile for this
time of year for this area). Meanwhile, regional VAD sites ahead
of the MCS depict 50 kts of 0-6 km shear and 100-200 m2/s2 0-3 km
SRH to support organized convection with embedded mesoyclones.
Going into this evening, the concern is for these developing
clusters to overlap with the forward propagating MCS to lengthen
residence times of intense rain rates. 

The biggest limiting factors to more robust flash flooding are dry
antecedent conditions and high FFGs. Soils across much of the area
are quite dry according to NASA SPoRT soil moisture percentiles,
while 3-6 hour aeral FFGs vary from 3-5 inches. However, recent
HREF probabilities show an elevated likelihood (40-60%) of 3
inches of rainfall across Southeast Georgia toward the Space Coast
through 3z, with a signal (10-25% chance) for 5 inches noted atop
the same area. This would suggest some instances of flash flooding
are possible, particularly atop hydrophobic urban areas.

Asherman

ATTN...WFO...CAE...CHS...FFC...JAX...MLB...TAE...TBW...

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

LAT...LON   33268187 32648069 31018116 29238077 28838150 
            29338241 29538323 30088456 31168466 32698319 
            

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