MESOSCALE PRECIPITATION DISCUSSION 0173
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
307 PM EDT THU JUL 03 2014

CORRECTED...FOR WORDING/TYPO
 
AREAS AFFECTED...ERN WV...VA...MD...PA...NY 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 031820Z - 040020Z
 
SUMMARY...INCREASING SHOWER AND THUNDERSTORM ACTIVITY IS EXPECTED
THROUGH THE AFTERNOON. MERGING AND LOCALIZED TRAINING OF CELLS
WILL ENHANCE THE THREAT FOR FLASH FLOODING.

DISCUSSION...THE LATEST VIS IMAGERY SHOWS AN INCREASINGLY AGITATED
AND EXPANDING CU/TCU FIELD FROM SOUTHWEST VA NORTHEAST UP ALONG
THE EASTERN FLANK OF THE APPALACHIANS AND NEAR THE BLUE RIDGE
INVOLVING EASTERN WV...VA...MD...PA AND NY. EMBEDDED WITHIN THE
GROWING CU/TCU FIELD ARE ALREADY CLUSTERS OF LOCALLY HEAVY SHOWERS
AND THUNDERSTORMS. ALL OF THIS ACTIVITY IS ALONG AND AHEAD OF A
QUASI-STATIONARY FRONT THAT IS AT LEAST TEMPORARILY HUNG UP OVER
THE APPALACHIANS. THE AIRMASS EAST OF THE FRONT IS BECOMING VERY
UNSTABLE...WITH SBCAPE VALUES OF 3000 TO 4000 J/KG...ESP ALONG AND
WEST OF THE I-95 CORRIDOR IN THE MID-ATLANTIC REGION.

STRONG DIURNAL HEATING THROUGH THE AFTERNOON COUPLED WITH A
TROPICAL AIRMASS ALREADY IN PLACE OVER THE MID-ATLANTIC AND
NORTHEAST...AND AIDED IN PART BY SOUTHERLY AND SOUTHEASTERLY WINDS
IN OFF THE ATLANTIC OCEAN NORTH OF HURRICANE ARTHUR...WILL FOSTER
VERY STRONG THERMODYNAMICS CONDUCIVE FOR WIDESPREAD AND ORGANIZED
HEAVY SHOWERS AND THUNDERSTORMS.

OVER THE NEXT SEVERAL HOURS THE BULK OF THE ACTIVITY SHOULD BE
GENERALLY WEST OF I-95 AND CONCENTRATED ESPECIALLY NEAR AND WEST
OF THE BLUE RIDGE. ALTHOUGH WITH SUCH STRONG INSTABILITY AND
APPROACH OF AN UPPER TROUGH FROM THE WEST...ACTIVITY SHOULD BEGIN
DEVELOPING EAST OF THE APPALACHIANS LATER IN THE AFTERNOON.

THERE IS STRONG CONCERN FOR CELL-MERGERS AND CELL TRAINING ACROSS
THE THREAT AREA...AND ESPECIALLY INVOLVING THE BLUE RIDGE OF
WESTERN VA...EASTERN WV...WESTERN MD...AND SOUTHWEST PA WHERE
ENHANCED LOW LEVEL CONFLUNCE/MOISTURE FLUX AND WEAK STEERING FLOW
AROUND THE NORTHWEST FLANK OF APPROACHING HURRICANE ARTHUR WILL
SUPPORT SLOW-MOVING AND TRAINING CELLS.

GIVEN THIS SET-UP AND PWATS AS PER LATEST GOES-SOUNDER OF 1.75 TO
2 INCHES...RAINFALL RATES WILL BE VERY INTENSE...AND LIKELY ON THE
ORDER OF 2 TO 3 INCHES/HR. THEREFORE...THE THREAT FOR FLASH
FLOODING WILL BE ELEVATED...AND ESP OVER AREAS OF HIGHER TERRAIN.
WILL CONTINUE TO MONITOR.

ORRISON

ATTN...WFO...OKX...ALY...PHI...BGM...AKQ...BUF...CTP...LWX...
RNK...

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

LAT...LON   40437844 41727761 43187681 43757587 43787469 43277389
            42377375 41537452 40407553 39487628 38047745 37177840
            36607932 36458043 36878076 38527937 40437844