MESOSCALE PRECIPITATION DISCUSSION 0368
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
415 PM EDT THU JUN 22 2017

AREAS AFFECTED...WESTERN & CENTRAL PA

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

VALID 222014Z - 222314Z

SUMMARY...SHORT-TERM FLASH FLOOD THREAT AS CONVECTION CONGEALS
ACROSS LOWER FFG VALUES

DISCUSSION...EXPERIMENTAL GOES-16 WV LOOP SHOWS A FAST MOVING
SHORTWAVE CROSSING THROUGH N NY WITH TRAILING EDGE OF THE
SHORTWAVE TROF CROSSING OUT OF LAKE ERIE PROVIDING MODEST DPVA FOR
ASCENT.  WEAK LOW LEVEL WAA FORCING FROM THE SOUTHWEST IS SLIGHTLY
CONVERGENT ACROSS WESTERN PA NEAR LIFTING FRONTAL ZONE COINCIDENT
WITH  POOL OF INCREASED INSTABILITY AND WEAKENED CAPPING DUE TO
FAIRLY CLEAR SKIES JUST NORTH OF CIRRUS OUTFLOW ACROSS S OH/WV
INTO MD.  THIS OUTFLOW JET IS ALSO FAVORABLY ORIENTED TO THE
DEVELOPING CONVECTION WITH LEFT EXIT PROVIDING ADDITION DIVERGENCE
(ALSO COUPLED WITH DISTANT RIGHT ENTRANCE OF STRONGER POLAR JET
ACROSS SE CANADA. 

IN THE LOWER LEVELS MOISTURE IS ALSO POOLED IN W PA WITH TPWS AOA
1.75"...WITH MODEST UNOBSTRUCTED INFLOW...FLUX TO PRODUCE MODEST
RAINFALL GENERATION WITH RATES UP TO 1.5"/HR.  FORWARD CELL
MOTIONS AND PROPAGATION E AND ESE SHOULD LIMIT DURATION;
HOWEVER...THE ORIENTATION OF THE CONVECTIVE DEVELOPMENT WILL
LIKELY SUPPORT SOME TRAINING...POTENTIALLY YIELDING TOTALS OF 2-3"
OVER THE NEXT 2-3 HOURS.  GIVEN ROUGH TERRAIN AND NATURALLY LOWER
FFG VALUES IN THE 1-1.5"/HR AND 1.5-2.0"/3HR ACROSS W PA INTO SW
CTP CWA...THERE IS A POSSIBLE THREAT FOR FLASH FLOODING TO OCCUR. 
WHILE COMPLEX MAY FURTHER MATURE/GROW INTO CENTRAL PA... GUIDANCE
VALUES RAPIDLY INCREASE GREATER THAN EVEN HIGHEST EXPECTED
RAINFALL RATES/3HR TOTALS...LESSENING THE THREAT WITH TIME.  

GALLINA

ATTN...WFO...CTP...PBZ...

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

LAT...LON   41537825 41397703 40587689 39847761 39797823
            40187902 40527998 40818010 41147944 41177888