MESOSCALE PRECIPITATION DISCUSSION 0408
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
154 PM EDT THU JUL 05 2018

AREAS AFFECTED...ERN/CTRL WV...NWRN VA...NRN/WRN MD...SRN PA

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 051753Z - 052345Z

SUMMARY...SCATTERED THUNDERSTORMS WERE DEVELOPING ALONG AND EAST
OF THE ALLEGHENY MOUNTAINS AS OF 130 PM EDT...AND THIS MAY
CONTINUE THROUGH THE AFTERNOON HOURS. ALTHOUGH STORMS MAY BE
SOMEWHAT LOCALIZED...THEY SHOULD PRODUCE VERY HEAVY RAIN
RATES...TO AROUND 2 IN/HR. THIS COULD PRODUCE FLASH FLOODING.

SUMMARY...REGIONAL RADARS AND GOES-16 SATELLITE IMAGERY SHOWED
GROWING CONVECTION ALONG AND NEAR THE ALLEGHENY MOUNTAINS FROM ERN
WV INTO SC PA. THESE STORMS WERE NOT MOVING
APPRECIABLY...ESPECIALLY IN ERN WV. GIVEN THE WEAKNESS IN UPPER
LEVEL FLOW ACROSS THE REGION NEAR THE CENTER OF THE RIDGE
AXIS...THERE IS A DISTINCT LACK OF SYNOPTIC FEATURES THAT WOULD
DRIVE THE CONVECTION OFF THE TERRAIN AND ALLOW IT TO PROPAGATE
MORE QUICKLY. THEREFORE...THIS INITIAL DEVELOPMENT MAY BE NEARLY
STATIONARY FOR SEVERAL HOURS AND LEAD TO SOME EPISODES OF FLASH
FLOODING IN THE SAME CORRIDOR (ERN/CTRL WV INTO SC PA). THE
ENVIRONMENT IS BOTH MODERATELY UNSTABLE (MLCAPE AROUND 1500-2000
J/KG) AND VERY MOIST (PWS 1.7 TO 2.0 INCHES) AND THIS SHOULD
SUPPORT ORGANIZED CONVECTION WITH RAIN RATES AROUND 2
IN/HR...POSSIBLY HIGHER THAN THAT IN AREAS OF STATIONARY
CONVECTION.

FURTHER EAST...THE ENVIRONMENT IS APPROXIMATELY THE SAME...BUT
CONVECTION HAS NOT DEVELOPED ALONG THE BLUE RIDGE MOUNTAINS
YET...ANOTHER PROMINENT SW-NE TERRAIN FEATURE IN THE REGION. THIS
MAY HAPPEN AS THE AFTERNOON WEARS ON...BUT CONFIDENCE IS LOWER
GIVEN LESS SUPPORT FROM HI-RES MODEL QPFS AND PROBABILISTIC OUTPUT
FROM THE 12Z HREF. SOME ISOLATED THUNDERSTORMS WERE ALSO NOTED
FROM NEAR BALTIMORE NORTH INTO SE PA. ALTHOUGH THESE WERE NOT TIED
TO A TERRAIN FEATURE...THEY WERE MOVING SLOWLY GIVEN WEAK FLOW
OVERALL...AND THUS COULD POSE A FLASH FLOOD THREAT GIVEN THE
SIMILAR ENVIRONMENT. CONFIDENCE IS AGAIN LOWER GIVEN A WEAKER
SIGNAL FROM THE HI-RES MODELS AS COMPARED TO AREAS FURTHER WEST
AND NORTHWEST ACROSS THE REGION.

AGAIN...THE MOST LIKELY AREA FOR FLASH FLOODING IN THE OUTLINED
DISCUSSION AREA IS ALONG THE ALLEGHENY MOUNTAINS AND PARTICULARLY
IN EASTERN WEST VIRGINIA. A FLASH FLOOD THREAT EXISTS FURTHER EAST
THIS AFTERNOON...BUT CONFIDENCE IS LOWER (AND IN THE ABSENCE OF
TERRAIN FEATURES...THERE MAY BE LESS TO LOCK CONVECTION INTO A
STATIONARY CONFIGURATION).

LAMERS

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

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

LAT...LON   41017713 41007630 40307560 39327621 39057707
            38537783 37337937 37168044 37668159 38498140
            39757948 40587814