MESOSCALE PRECIPITATION DISCUSSION 0705
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
604 PM EDT FRI AUG 18 2017

AREAS AFFECTED...ERN MID-ATLANTIC STATES & SRN NEW ENGLAND

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

VALID 182203Z - 190403Z

SUMMARY...OCCASIONAL CELL TRAINING ALONG A MOVING LINE OF
CONVECTION IS EXPECTED TO LEAD TO HOURLY RAIN TOTALS TO 2" AND
LOCAL AMOUNTS TO 4" OVER THE NEXT SEVERAL HOURS.

DISCUSSION....THUNDERSTORMS CONTINUE TO BUILD FROM NORTHERN VA
NORTHEAST INTO SOUTHERN UPSTATE NY NEAR AND AHEAD OF AN OUTFLOW
BOUNDARY PRECEDING A COLD FRONT.  PRECIPITABLE WATER VALUES ARE
1.7-2.3" IN THE AREA.  INFLOW AT 850 HPA IS SOUTHWEST AT 25-30
KTS, WHICH IS ADVECTING 1000-3000 J/KG OF MLCAPE INTO THE REGION. 
EFFECTIVE BULK SHEAR OF 30-40 KTS ALONG WITH THE UNIDIRECTIONAL
FLOW WITH HEIGHT IS LEADING TO A LINEAR CONVECTIVE FEATURE WITH
SOME OCCASIONAL CELL TRAINING CHARACTER.

THE MESOSCALE GUIDANCE HAS A GENERAL SIGNAL FOR HEAVY RAINFALL IN
PORTIONS OF THE MID-ATLANTIC STATES AND SOUTHERN NEW ENGLAND, WITH
LOCAL AMOUNTS TO 4" BEING FORECAST.  RADAR ESTIMATES WITHIN AREAS
OF TRAINING HAVE BEEN IN THE 2" AN HOUR BALLPARK, WHICH IS
EXPECTED TO CONTINUE AS THE LINE MOVES EAST AT ~25 KTS.  SOILS ARE
PARTIALLY SATURATED AS A BULK OF THE MID-ATLANTIC REGION HAS SEEN
100-400% OF NORMAL RAINFALL DURING THE PAST 30 DAYS. AND A GOOD
DEAL OF THIS REGION IS URBANIZED.  FLASH FLOODING IS POSSIBLE.

ROTH

ATTN...WFO...AKQ...ALY...BGM...BOX...CTP...LWX...OKX...PHI...

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

LAT...LON   42727046 42417080 42127049 41317046 40837208
            40377372 39427413 38667479 38037515 37587588
            37597674 38267776 39067765 40397601 41887434
            42547179