Flash Flood Guidance
Issued by NWS

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000
AWUS01 KWNH 302100
FFGMPD
NCZ000-SCZ000-GAZ000-TNZ000-010100-

MESOSCALE PRECIPITATION DISCUSSION 0157
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
459 PM EDT SAT APR 30 2016

AREAS AFFECTED...NORTHEAST GA & THE WESTERN CAROLINAS

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

VALID 302100Z - 010100Z

SUMMARY...CONVECTIVE DEVELOPMENT SHOULD BECOME MORE WIDESPREAD AND
MORE EFFICIENT OVER THE NEXT FOUR HOURS.  HOURLY RAIN RATES UP TO
1.75", WITH LOCAL AMOUNTS OF 2-4", COULD LEAD TO FLASH FLOODING.

DISCUSSION...CONVECTION HAS BEGUN TO BECOME MORE CONCENTRATED OVER
NORTHEAST GA AND NORTHWEST SC OVER THE PAST HOUR, WITH COOLING
CLOUD TOPS SEEN ON RECENT SATELLITE IMAGERY.  THIS IS OCCURRING
OVER THE TOP OF A COUPLE WEAK OUTFLOW BOUNDARIES IN THE VICINITY
OF A STATIONARY FRONT.  MLCAPES ARE 1000-2000 J/KG ACROSS
NORTHWEST GA, WHILE 850 HPA INFLOW IN CONVERGENT AT ~ 20 KTS FROM
THE SOUTH.  IN SPOTS, 25 KTS OF CLOUD BASE INFLOW EXISTS AS SOME
OBSERVATIONS IN THE AREA SHOW A LIGHT EAST WIND.  PRECIPITABLE
WATER VALUES OF ~1.4" EXIST HERE PER GPS VALUES.

THE 12Z GFS-BASED GALVEZ-DAVISON INDEX INDICATES CONVECTIVE
COVERAGE SHOULD EXPAND OVER THE NEXT SEVERAL HOURS AT INFLOW AT
850 HPA INCREASES BRINGING PRECIPITABLE WATER VALUES UP TO
1.50-1.75".  HOWEVER, MUCAPES IN THE REGION SHOULD BE ON A
DOWNWARD TREND AFTER SUNSET, THOUGH THIS IS ALSO PARTIALLY DUE TO
EXPECTED CONVECTIVE ACTIVITY IN THE MEANTIME, WITH RECENT RAP
FORECASTS INDICATING MUCAPE BECOMING SIGNIFICANTLY ERODED AFTER
01Z.  WITH INCREASING LOW-LEVEL INFLOW, BACKBUILDING CONVECTION IS
POSSIBLE ACROSS NORTHERN GA, AND CELL MERGERS ARE POSSIBLE SHOULD
ANY ORGANIZED CELLS DEVELOP.  THE MEAN 850-400 HPA WIND INDICATES
PULSE CONVECTION WOULD MOVE NORTHEAST AT ~25 KTS WHILE ORGANIZED
CLUSTERS MOVE MORE EASTERLY AT ~20 KTS.  HOURLY RAIN RATES UP TO
1.75", ALONG WITH LOCAL AMOUNTS IN THE 2-4" RANGE INDICATED BY
MOST OF THE MESOSCALE GUIDANCE IN THIS AREA, WOULD APPROACH THREE
HOUR LOCAL FLASH FLOOD GUIDANCE VALUES AND COULD LEAD TO FLASH
FLOODING WITHIN RUGGED TERRAIN.

ROTH

...PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...CAE...FFC...GSP...MRX...

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

LAT...LON   36008265 35808190 35468144 35018149 34298176
            33788238 33668334 33998424 34568484 35148425
            35728358



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