MESOSCALE PRECIPITATION DISCUSSION 0256
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1027 AM EDT FRI AUG 08 2014
 
AREAS AFFECTED...EASTERN TN...WESTERN NC...NORTHWEST SC...NORTHERN
GA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 081425Z - 081845Z
 
SUMMARY...SLOW-MOVING AND REPEATING WARM-TOPPED CONVECTION WILL
FOSTER INTENSE RAINFALL RATES AND POTENTIALLY EXCESSIVE TOTALS
THROUGH MIDDAY.

DISCUSSION...A WELL-DEFINED MCV AND ASSOCD SFC LOW CENTER OVER SRN
IL THIS MORNING IS VERY SLOWLY MOVING EASTWARD ALONG A FRONTAL
ZONE INVOLVING THE OH/TN VALLEYS. THE FRONT ACTUALLY EXTENDS SEWD
INTO CNTRL GA AND THEN EAST INTO THE SOUTHEAST COASTAL PLAIN.
MEANWHILE...A LARGE AREA OF DEEP MOISTURE WITH PWATS NEAR 2 INCHES
ARE POOLED ALONG AND JUST NORTH OF THE FRONT AS PER LATEST
GPS-DERIVED PWATS ARE NEAR 2 INCHES.

MODEST LOW LEVEL SWLY FLOW UP TO ABOUT 20 KTS IS OVERRUNNING THE
BNDRY...BUT THERE IS SUFFICIENT ELEVATED CAPE GIVEN THE LARGER
SCALE FORCING AHEAD OF THE MCV FOR NUMEROUS SHWRS/TSTMS. THE
ACTIVITY IS TENDING TO REPEAT GIVEN THE PERSISTENT LOW LVL FEED OF
MOIST/UNSTABLE AIR FROM THE TN VLY.

THE ONGOING CONVECTION IS WARM-TOPPED IN NATURE...AND AS A RESULT
RAINFALL PRODUCTION WILL BE PARTICULARLY EFFICIENT AND GIVEN THE
VERY HIGH PWAT ENVIRONMENT...RAINFALL RATES WILL BE QUITE INTENSE.
ALREADY RAINFALL RATES UPWARDS OF 2 INCHES/HR HAVE BEEN
NOTED...AND GIVEN THE SLOW-MOVEMENT AND REPETITIVE NATURE TO THE
CONVECTION...THERE WILL BE CONCERN FOR EXCESSIVE AMTS THROUGH
MIDDAY.

THE LATEST HI-RES MODEL GUIDANCE IS GENERALLY NOT HANDLING THE
CURRENT ACTIVITY TOO WELL...WITH THE 06Z NAM-CONEST AND 09Z HRRR
CONSIDERABLY UNDERDONE WITH THE CONVECTIVE COVERAGE. THE 00Z ARW
AND 00Z NMMB ARE AT LEAST BETTER IN IDENTIFY THE RELATIVE
PLACEMENT OF CONVECTIVE BANDS.

EXPECT THE ACTIVITY TO PERSIST FOR THE NEXT FEW HOURS AT LEAST AND
ESP WITH THE AID OF OROGRAPHIC FORCING. FLASH FLOODING WILL BE
POSSIBLE.

ORRISON

ATTN...WFO...RNK...GSP...MRX...FFC...

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

LAT...LON   35668458 35738412 35818323 36488191 36388134 35658143
            34688194 34108247 34108354 34338420 34748488 35068518
            35458497 35668458