Mesoscale Precipitation Discussion 0569
NWS Weather Prediction Center College Park MD
327 PM EDT Tue Jul 31 2018

Areas affected...N/C Georgia, EC Alabama, Upstate South Carolina

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

Valid 311926Z - 010000Z

Summary...Increasingly widespread thunderstorms will affect
northern Georgia and adjacent areas this afternoon and into the
early evening hours. Locally heavy rainfall is likely, and in some
cases this could lead to flash flooding. Rain rates up to 2-3
in/hr will be possible.

Discussion...Regional radars showed an increasing concentration of
convection centered on north Georgia, roughly along a ALX-ATL-GSP
axis. This appeared to be a combination of convection and outflows
lifting north having initiated closer to the Gulf sea breeze
earlier in the day, and convection initiating just ahead of a
stalling surface front (with more of an eastward drift). This was
leading to a confluence of convective clusters and lines in
northern Georgia; therefore, radar and satellite trends alone
suggest a concentrated area of heavy rainfall potential late this
afternoon.

RAP analysis indicates strong instability with MLCAPE values
around 2000-2500 j/kg. Even modifying RAP soundings for surface
observations in rain-cooled locations in the wake of ongoing
thunderstorms (around 72/70) yields 1500 j/kg MLCAPE with limited
CINH and only a very shallow stable layer near the surface.
Therefore, it is not surprising to see some continued convective
growth upstream from areas that have already experienced rain this
afternoon, and this may continue given the WSW flow at 925-850mb,
observed on the FFC, BMX, and HTX radar VWPs. With the potential
for backbuilding convection, localized training, and slow storm
motions, the risk of heavy rainfall should be increased. PW values
approaching 2 inches should support rain rates up to 2-3 in/hr
with the strong instability and slow and/or chaotic storm motions
and mergers. This could lead to flash flooding, particularly if
focused over an urban area.

Lamers

ATTN...WFO...BMX...CAE...FFC...GSP...TAE...

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

LAT...LON   34828335 34438195 33028299 31998430 31698533
            32538628 33668607 34458511