MESOSCALE PRECIPITATION DISCUSSION 0573
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
625 PM EDT WED AUG 17 2016
 
AREAS AFFECTED...ERN WV...NRN VA...MD 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 172224Z - 180400Z
 
SUMMARY...REPEATING ROUNDS OF HEAVY RAIN ALONG WITH CELL MERGERS
WILL HAVE THE POTENTIAL TO PRODUCE LOCALIZED 3-4 INCH RAINFALL
TOTALS FROM THE WV/VA BORDER INTO CNTRL-NRN VA...DC AND MD. THE
BEST FLASH FLOOD POTENTIAL WILL BE LIMITED TO URBAN AREAS AND
LOCATIONS WITH RECENT HEAVY RAINFALL FROM THE PAST WEEK...LIMITING
THE COVERAGE OF FLASH FLOODING.

DISCUSSION...SURFACE OBSERVATIONS AT 22Z SHOWED HIGHER
TEMPERATURE/DEWPOINT TEMPERATURES ACROSS SRN AND CNTRL VA COMPARED
TO LOCATIONS FARTHER NORTH DUE TO THE PRESENCE OF THE TAIL END OF
A COLD FRONT ACROSS THE AREA. THIS GRADIENT IN THETA-E IS
REFLECTED IN MLCAPE VALUES WITH AN ESTIMATED 500-1000 J/KG ACROSS
NRN MD VERSUS CLOSER TO 2000 J/KG NEAR I-64 AS OF 22Z. DESPITE THE
WEAKER INSTABILITY ACROSS NRN LOCATIONS HOWEVER...FORCING AHEAD OF
A 700 MB SHORTWAVE TROUGH IS EXPECTED TO OVERSPREAD THE WV
PANHANDLE INTO NRN VA AND MD OVER THE NEXT 3-6 HOURS ACCOMPANIED
BY A SLIGHT SURGE IN LOW LEVEL MOISTURE...WHILE LOCATIONS FARTHER
SOUTH WILL SEE LESS OF A DIRECT IMPACT FROM THE SHORTWAVE. 

ESTIMATED STORM MOTIONS WILL BE OFF TO THE ENE AT 15-25 KTS...AND
UNIDIRECTIONAL FLOW THROUGHOUT THE CLOUD BEARING LAYER WILL
PROMOTE REPEATING CELL MOTIONS WITH SOME TRAINING GIVEN SIMILAR
MAGNITUDE OF THE 850-700 MB FLOW. WHILE RELATIVELY WEAK LOW LEVEL
FLOW IS EXPECTED TO KEEP STORMS LARGELY PROGRESSIVE...CELL MERGERS
AND A FEW REPEATING ROUNDS OF HEAVY RAIN MAY PRODUCE A FLASH FLOOD
THREAT ACROSS URBAN LOCATIONS AND AREAS THAT PICKED UP HEAVY RAIN
OVER THE PAST SEVERAL DAYS GIVEN GREATER SOIL MOISTURE. GENERALLY
THOUGH...THE FLASH FLOOD THREAT IS EXPECTED TO BE ISOLATED.

OTTO

ATTN...WFO...AKQ...CTP...LWX...PBZ...PHI...RLX...RNK...

ATTN...RFC...MARFC...OHRFC...

LAT...LON   39837819 39777677 39567603 38947565 38167621 
            37797769 37997933 38688007 39448014 39687948