Graphic for MPD #0672

MESOSCALE PRECIPITATION DISCUSSION 0672
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
100 PM EDT SAT AUG 12 2017

AREAS AFFECTED...CNTRL/ERN PA INTO NJ AND FAR SRN NY

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

VALID 121700Z - 122300Z

SUMMARY...RAINFALL RATES OF 1-2 IN/HR ARE EXPECTED TO IMPACT
PORTIONS OF CNTRL AND ERN PA INTO NJ AND FAR SRN NY THROUGH THE
AFTERNOON. GIVEN WET ANTECEDENT CONDITIONS...FLASH FLOODING WILL
BE POSSIBLE.

DISCUSSION...REGIONAL RADAR IMAGERY SHOWED SHOWERS AND
THUNDERSTORMS DEVELOPING AHEAD OF A COLD FRONT WHICH EXTENDED
SSWWD THROUGH WRN NY...WRN PA AND WV AT 16Z. LOOPS OF VISIBLE
IMAGERY SHOWED DECREASING AREAS OF CLOUD COVER AHEAD OF THE COLD
FRONT OVER CNTRL TO ERN PA WHICH HAS ALLOWED MLCAPE TO GROW INTO
THE 500-1000 J/KG RANGE ACCORDING TO DATA FROM THE LATEST SPC
MESOANALYSIS PAGE. FURTHER INCREASES IN CAPE ARE EXPECTED IN THE
SHORT TERM AS TEMPERATURES LIKELY RISE INTO THE LOW 80S IN A FEW
LOCATIONS. GPS DATA AND 12Z AREA SOUNDINGS SHOWED A RATHER STRONG
GRADIENT IN PRECIPITABLE WATER AS ONE MOVES SOUTH FROM NRN
PA...1.25 INCHES...TO SERN PA...1.75 INCHES. THIS GRADIENT IS
REPRESENTED WELL IN RAP ANALYSES.

AS ONGOING CONVECTION AHEAD OF THE COLD FRONT IN W-CNTRL PA
ADVANCES EAST OVER THE NEXT FEW HOURS AND MEETS WITH ADDED DAYTIME
HEATING AND LOCALLY HIGHER MOISTURE VALUES...RAINFALL RATES OF 1-2
IN/HR WILL BE POSSIBLE. WHILE RAP FORECAST KINEMATIC PROFILES
SUPPORT A GENERAL EWD MOVEMENT OF STORMS AT ABOUT 20 KT...THE
POTENTIAL WILL EXIST FOR BRIEF REPEATING CELL MOTIONS AND MERGERS
WHICH WOULD ALLOW FOR HEAVY RAINFALL OVER A REGION WHICH HAS SEEN
ABOVE AVERAGE RAINFALL OVER THE PAST 1-2 WEEKS...MOST NOTABLY A
STRIPE OF 1-3 INCHES WHICH FELL NEAR THE I-78 CORRIDOR FROM CXY TO
NORTH OF ABE INTO NRN NJ OVER THE PAST 24 HOURS.

THE FLASH FLOOD THREAT FOR LOCATIONS FARTHER NORTH TOWARD THE
NY/PA BORDER...AN AREA WHICH ALSO HAS LOWER FFG...SHOULD BE TOO
ISOLATED TO SUPPORT COVERAGE IN THE MPD THREAT AREA. STORM MOTIONS
SHOULD BE SLIGHTLY FASTER THAN THOSE TO THE SOUTH AND THE AREA
WILL HAVE LOWER AVAILABLE MOISTURE INTO THE AFTERNOON.

OTTO

ATTN...WFO...BGM...CTP...OKX...PHI...

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

LAT...LON   41717498 41627459 41327424 41137404 40667418
            40387444 39957492 39967638 39897764 39987826
            40127847 40397850 40607827 40777776 41217690
            41407633 41437625 41687547 41697541


Last Updated: 100 PM EDT SAT AUG 12 2017