MESOSCALE PRECIPITATION DISCUSSION 0332
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1049 AM EDT SAT JUN 17 2017

AREAS AFFECTED...SOUTHWEST PA TO NORTHWEST NC

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

VALID 171448Z - 172048Z

SUMMARY...THUNDERSTORMS ARE EXPECTED TO FORM LATER THIS MORNING
INTO THIS AFTERNOON NEAR THE BLUE RIDGE MOUNTAINS AND TERRAIN OF
EASTERN WV.  HOURLY RAIN RATES TO 1.75", WITH LOCAL AMOUNTS TO 3",
ARE EXPECTED.

DISCUSSION...IN THE WAKE OF AN MCV SPAWNED BY CONVECTION IN
SOUTHWEST VA LAST NIGHT, SKIES ARE PARTLY SUNNY ACROSS WESTERN VA
AND EASTERN WV.  RECENT VISIBLE IMAGERY SHOWS THE FIRST TOWERING
CUMULI FORMING IN EASTERN WV.  A NARROW SHORTWAVE ALOFT/AREA OF
DARKENING ON WATER VAPOR IMAGERY EXTENDS FROM SOUTH-CENTRAL PA
INTO CENTRAL WV.  THE 850 HPA WIND FLOW IS PARALLEL TO THE
MOUNTAIN CHAINS AT 10-15 KTS PER VAD WIND PROFILES.  THE 12Z
SOUNDING FROM BLACKSBURG VA SHOWS NEARLY UNIDIRECTIONAL FLOW WITH
HEIGHT EXTENDING UP TO THE 300 HPA PRESSURE LEVEL.  PRECIPITABLE
WATER VALUES ARE ~1.5", AND THE REGION IS IN AND NEAR A
MOISTURE/WEAK TEMPERATURE GRADIENT WITH HIGHER VALUES TO THE EAST.
MLCAPE VALUES ARE CURRENTLY ~250 J/KG.

THE EXPECTATION IS FOR THUNDERSTORMS TO BUILD AS INSTABILITY
INCREASES DUE TO DAYTIME HEATING -- MLCAPE VALUES SHOULD RISE
~1000 TO 1500 J/KG.  THUNDERSTORMS ARE EXPECTED TO BE PULSE IN
NATURE, SIMILAR TO YESTERDAY, AND INITIALLY MOVE UP THE TOPOGRAPHY
BEFORE TRYING TO SHIFT SOMEWHAT EASTWARD INTO THE VALLEYS THIS
AFTERNOON AS INSTABILITY ERODES.  THE MAIN THREATS ARE SHORT
PERIODS OF CELL TRAINING WITHIN THIS FLOW REGIME AND CELL MERGERS.
 FLASH FLOOD GUIDANCE VALUES INDICATE INCREASINGLY SATURATED SOILS
DUE TO THE PAST FEW DAYS OF LOCALLY HEAVY RAIN.  HOURLY RAIN RATES
UP TO 1.75" WITH LOCAL AMOUNTS UP TO 3" ARE EXPECTED.  THE 06Z
SSEO NEIGHBORHOOD PROBABILITIES OF EXCEEDING THE THREE HOUR FLASH
FLOOD GUIDANCE VALUES EXCEED 50% FROM SOUTHWEST PA INTO NORTHWEST
NC, WITH THE STRONGEST (90%+) SIGNAL NEAR LANSING NC BY 18Z WHERE
THE HIGHEST AMOUNTS OF INSTABILITY MAY BE AVAILABLE AT THE TIME. 
FLASH FLOODING IS A CONCERN.

ROTH

ATTN...WFO...CTP...GSP...LWX...MRX...PBZ...RAH...RLX...RNK...

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

LAT...LON   40487805 40087728 38947788 37867866 37137941
            36128022 35998109 35898196 36098211 36848188
            37628121 38318072 38838015 39607956 40127900