MESOSCALE PRECIPITATION DISCUSSION 0567
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EDT WED JUL 26 2017

AREAS AFFECTED...SOUTHEAST GA....EXT NORTHEAST FL

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 261800Z - 262300Z

SUMMARY...VERY SLOW EXTREMELY EFFICIENT RAINFALL WITH RATES UP TO
3"+/HR ARE POSSIBLE POTENTIALLY LEADING TO LOCALIZED FLASH
FLOODING CONCERNS.

DISCUSSION...COMPACT SHORTWAVE/CONVECTIVELY MAINTAINED MCV IS WELL
DEFINED IN SATELLITE ACROSS SE GA...THOUGH IS A BIT MORE ELONGATED
NEAR THE SURFACE TO 850 WITH TROF EXTENDING NORTHWARD ALONG THE SC
COAST TOWARD SECONDARY WAVE OFF SHORE.  IT IS OUTFLOW AND SUPPORT
FROM THE SECONDARY WAVE TO SUPPLY SUFFICIENT LOW LEVEL CONVERGENCE
TO BREAK THE WEAK CAP IN THE AREA.

WHILE RAP ANALYSIS SUGGESTS THAT THERE IS AN INSTABILITY MINIMA
NEAR THE CENTER OF THE MCV THIS BELIES THE FACT THE LAPSE RATES
ARE NEARLY FULLY MOIST ADIABATIC THROUGH MUCH OF THE TROPOSPHERE
WITH TPWS OVER 2.25" BUT NARROW SKINNY PROFILES THAT SUPPORT EVEN
1500 J/KG OF MLCAPE...WHILE THE PERIPHERY WHERE DRIER MID-LEVELS
SUPPORT VALUES TO 3000 J/KG.   THESE SATURATED PROFILES NEAR THE
INNER CORE WILL HAVE TWO FACTORS GOING FOR IT: LIMITED DRY AIR
LIMITS COLD POOL/STRONG OUTFLOW TO PROPAGATE AS WELL AS WARM CLOUD
PROCESSES THAT WILL SUPPORT GREATER THAN 3"/HR RATES. THIS HAS
BEEN SUPPORTED BY BACKYARD OBSERVATION NETWORK RATES SOUTHEAST OF
RICEBORO,GA OF 2"/30 MINUTES WHICH WAS CONFIRMED BY MULTIPLE
OBSERVATIONS.

THE LAST CONCERN FOR FLOODING IS RELATED TO VERY SLOW CELL
MOTIONS...IN FACT NEAR ZERO NEAR WAYCROSS, GA.  STILL SLOW
SOUTH/SOUTHWEST MOTION OF THE MCV SHOULD ALLOW FOR SOME MOVEMENT
OF THE INDIVIDUAL CELLS THOUGH LIKELY AT AROUND 5-10KTS AT MOST. 
THIS COULD POSE TOTALS OVER 3-4" IN 1-2 HOURS. 
ADDITIONALLY...REDEVELOPMENT IS POSSIBLE OVER THE SAME AREA
PARTICULARITY ALONG THE GA/EXT NE FL COAST WHERE RIGHT
QUADRANT/DOWN SHEAR PROFILES SHOULD SUPPORT BETTER/MORE CONSISTENT
MOISTURE CONVERGENCE. 

THE MOST LIMITING FACTOR FOR FLASH FLOODING IS OBVIOUSLY THE
GROUND CONDITIONS...WHILE GENERALLY FLAT EVEN SWAMPY SUCH AS THE
OKEFENOKEE WILDERNESS AND AS SUCH FFG VALUES MAY BE DIFFICULT TO
EXCEED WITH EXCEPTION TO 1HR/QUICK BURST RATES.   THOUGH SOME
AREAS RECEIVED SCATTERED 1-2+" TOTALS YESTERDAY PERHAPS INCREASING
RUNOFF LOCALLY. ALL CONSIDERED FLASH FLOODING IS ONLY CONSIDERED
POSSIBLE. 

GALLINA

ATTN...WFO...CHS...FFC...JAX...TAE...

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

LAT...LON   32488234 32418152 32008115 31698103 31258119
            30798133 30468128 30228134 30198178 30588242
            30838274 31168305 32038288