MESOSCALE PRECIPITATION DISCUSSION 0113
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
939 PM EDT MON APR 23 2018
AREAS AFFECTED...GEORGIA...EXT. WESTERN SOUTH CAROLINA
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE
VALID 240137Z - 240600Z
SUMMARY...NEAR ZERO CELL MOTIONS WITH MODEST TO HVY RAIN RATES
POSE WIDELY SCATTERED FLASH FLOODING RISK THROUGH EARLY OVERNIGHT
PERIOD.
DISCUSSION...GOES-16 WV SUITE DEPICTS A DEEPLY STACKED UPPER LOW
WELL NORTHWEST IN WESTERN KY WITH STRONG WARMING INDICATIVE A
STRONG JET ACROSS WESTERN GULF COAST. A SUBTLE SHORTWAVE/PIVOT IN
THE MID-LEVEL FLOW EXISTS AROUND COLUMBUS,GA AND VERTICALLY VEERED
WIND PROFILES SUPPORT SOLID DPVA AND DIFFLUENCE FOR MAINTENANCE OF
UPDRAFTS WHILE ALSO SUPPORTING ROTATING UPDRAFTS. GIVEN PLACEMENT
OF THE JET...PROPAGATION VECTORS ARE ABOUT 5-10KTS AND EXPECTED TO
SLACKEN FURTHER AS THE JET STREAK UNDERCUTS THE AREA OF CONCERN.
COMPOUND THIS WITH SLOWED CELL MOTIONS DUE TO SUPERCELLULAR NATURE
ALLOWS FOR NEARLY STATIONARY CONVECTION.
MOISTURE ENVIRONMENT DOES NOT SCREAM OF HIGH RAINFALL EFFICIENCY
DUE TO DRY POCKET AT 7-5H ADVECTING NE ACROSS SW GA. HOWEVER, SFC
TO 800MB ADVECTED ON EASTERLY FLOW WITH TDS IN MID TO UPPER 60S
AND 11-12C AT 850MB WITH SOLID MOISTURE CONVERGENCE/CONFLUENCE
ESPECIALLY NEAR THE DEVELOPING SURFACE LOW IN CENTRAL GA. THIS
LEADS TO TPW VALUES UP TO 1.5" IN THE LOWEST LEVELS BUT SLOW CELL
MOTIONS AND STRONG UPDRAFTS FROM CAPES MLCAPES TO 500-1000 J/KG
(1500 OVER SE GA) SUGGEST PROFILES CAN BE MOISTENED FAIRLY QUICKLY
TO SUPPORT RAINFALL EFFICIENCY TO 1.5". WHILE RADAR ESTIMATES ARE
LIKELY A BIT HIGH GIVEN SOME HAIL CONTAMINATION... THE ABUNDANCE
OF SMALL HAIL MAY ACTUALLY HELP IN OVERALL WATER TOTALS OR EVEN
GROUND FLOW CHOKE POINTS FOR FLOODING CONCERNS. HI-RES CAMS ARE
SUPPORTIVE OF THIS EVOLUTION PARTICULARLY THE ARW/HRRR AND HRRRV3
(THOUGH DISPLACED NORTHWEST A BIT) AND SUGGEST 1-2 HOURS OF 1.5-2"
RATES AND TOTALS OF 3-4" POSSIBLE VERY CLOSE TO LOCAL FFG VALUES.
CURRENT RADAR/EIR LOOP SHOWS GREATEST THREAT FOR FLASH FLOODING
ALONG A FAVORABLY ORIENTED CONVERGENCE BOUNDARY FROM BURKE/SCREVEN
COUNTY TO IRWIN/BEN HILL COUNTY MAY FURTHER SUPPORT TRAINING EVEN
AS CELL MOTIONS ARE SLOW TO THE NORTHEAST.
STILL OVERALL COVERAGE THREAT WILL BE VERY LIMITED GIVEN THE
MID-LEVEL DRYING BUT CELLS THAT DO DEVELOP POSE AT LEAST A
LOCALIZED FLASH FLOOD RISK THROUGH THE EARLY EVENING..ESPECIALLY
SOUTH AND EAST...GIVEN BEST MAINTAINED LOW LEVEL MOISTURE AND
INSTABILITY THROUGH THE EARLY OVERNIGHT HOURS.
GALLINA
ATTN...WFO...CAE...CHS...FFC...GSP...JAX...TAE...
ATTN...RFC...SERFC...
LAT...LON 34258316 34048211 33658140 32928088 32448091
31658175 31388261 31428307 31898321 32548314
33058342 33238369 33048468 33718492 34168451
Last Updated: 939 PM EDT MON APR 23 2018