MESOSCALE PRECIPITATION DISCUSSION 0622
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
451 PM EDT FRI AUG 04 2017

AREAS AFFECTED...FAR EASTERN OH...NORTHERN WV...WESTERN
MD...PA...NY...VT...WESTERN NH...FAR WESTERN MA

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

VALID 042050Z - 050250Z

SUMMARY...NUMEROUS SHOWERS AND THUNDERSTORMS ARE EXPECTED THROUGH
THE EVENING HOURS WITH SOME LOCALLY VERY HEAVY RAINFALL. SOME
FLASH FLOODING CANNOT BE RULED OUT.

DISCUSSION...THE LATEST GOES-WV/IR SATELLITE IMAGERY SHOWS A
STRONG UPPER TROUGH TAKING ON A NEGATIVE TILT AS IT CROSSES THE
GREAT LAKES REGION AND PORTIONS OF THE UPPER OH VALLEY THIS
AFTERNOON. THIS IS FOSTERING ROBUST LARGE SCALE DYNAMICS/FORCING
ALONG AND OUT AHEAD OF AN ASSOCIATED COLD FRONT THAT IS QUICKLY
ADVANCING EAST TOWARD THE NORTHERN MID-ATLANTIC STATES AND THE
NORTHEAST. ALREADY THERE ARE NUMEROUS SHOWERS AND THUNDERSTORMS
ALONG AND AHEAD OF THE COLD FRONT AS THE DYNAMICS/LARGE SCALE
SHEAR FOSTERED BY THE UPPER TROUGH INTERACTS WITH A MOIST AND
UNSTABLE BOUNDARY LAYER. IN FACT...PWATS ARE GENERALLY 1.5 TO 1.75
INCHES WITH MLCAPE VALUES OF AS MUCH AS 1500 TO 2000 J/KG.

THE PROGRESSIVE NATURE OF THE CONVECTION TO THIS POINT HAS
GENERALLY PRECLUDED THERE BEING MUCH OF A FLASH FLOOD THREAT...BUT
OVER THE NEXT FEW HOURS THERE WILL BE CLUSTERS OF MULTI-CELL
CONVECTION THAT MAY BEGIN TO MERGE TOGETHER AND BECOME A BIT MORE
ORGANIZED AS THE UPSTREAM TROUGH CONTINUES TO ADVANCE EAST AND
AMPLIFY. SOME REPEATING OF CONVECTIVE CELLS WILL BE POSSIBLE AS
WELL...AND THE COMBINATION OF THIS AND CELL-MERGERS MAY RESULT IN
SOME GROWING CONCERN FOR POCKETS OF FLASH FLOODING. RAINFALL
AMOUNTS OF TO 2 INCHES/HR ARE POSSIBLE...WITH SOME LOCALIZED STORM
TOTALS OF 3 TO 4 INCHES.

THIS IN PARTICULAR MAY CAUSE SOME CONCERNS OVER AREAS OF HIGHER
TERRAIN INVOLVING PARTS OF THE CENTRAL AND NORTHERN APPALACHIANS
FROM NORTHERN WV/WESTERN MD POINTS NORTHEAST UP ACROSS
WEST-CENTRAL PA AND CENTRAL/SOUTHERN NY. SOME OF THESE AREAS HAVE
SEEN VERY HEAVY RAINFALL OVER THE LAST WEEK...AND SO THE SOIL
CONDITIONS WILL BE LOCALLY SENSITIVE TO THESE ADDITIONAL AMOUNTS.

ATTN...WFO...ALY...BGM...BOX...BTV...BUF...CLE...CTP...GYX...
LWX...OKX...PBZ...PHI...RLX...

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

LAT...LON   45057291 45037176 44657126 43767143 42747224
            41937343 40777534 40027693 39517767 39207858
            39067986 39408078 39928109 40778103 41788045
            42108016 42357987 42677924 43307908 43417837
            43387758 43467696 43617647 44177630 44757577
            45027489