MESOSCALE PRECIPITATION DISCUSSION 0521
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
413 AM EDT MON JUL 23 2018

AREAS AFFECTED...CENTRAL PA

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

VALID 230812Z - 231112Z

SUMMARY...THUNDERSTORMS TO THE WEST OF A WARM FRONT SHOULD PERSIST
FOR ANOTHER FEW HOURS WHILE SHIFTING FARTHER WEST AND NORTH. 
HOURLY RAIN TOTALS TO 1.5" AND LOCAL AMOUNTS TO 3" ARE EXPECTED.

DISCUSSION...A MERIDIONALLY-ORIENTED BAND OF SHOWERS AND
THUNDERSTORMS CONTINUES JUST TO THE WEST OF A WARM FRONT ADVANCING
THROUGH EASTERN PA.  AN APPROACHING CONVECTIVE VORTICITY MAXIMUM
ACROSS WEST-CENTRAL VA AND AN UPPER LOW OVER SOUTHEAST ONTARIO ARE
THE LEADING CANDIDATES FOR INCREASING DIVERGENCE ALOFT.  IN THE
WARM SECTOR, ML CAPE VALUES OF 1000-1500 J/KG CONTINUE TO RESIDE;
CIN REMAINS MINIMAL.  PRECIPITABLE WATER VALUES OF 1.7-2" EXIST
PER GPS DATA.  INFLOW AT 850 HPA IS 20-25 KTS OUT OF THE SOUTH,
WHILE EFFECTIVE BULK SHEAR OF 30-40 KTS COMBINED WITH
UNIDIRECTIONAL FLOW HAS ORGANIZED THE ACTIVITY INTO A RAIN BAND.

THE MESOSCALE GUIDANCE HAS SOME GRASP ON EXPECTATIONS HERE, WHICH
INDICATES THAT ISSUES SHOULD FADE BEYOND 11Z, WHICH COULD EITHER
BE DUE TO DECLINING INSTABILITY OR DEVELOPING CIN.  THE WARM FRONT
IS EXPECTED TO RETROGRADE SLIGHTLY MORE OVER THE NEXT FEW HOURS,
WHICH SHOULD SHIFT THE THUNDERSTORMS MORE WEST AND NORTHWARD WITH
TIME.  HOURLY RAIN TOTALS TO 1.5" ARE ESTIMATED BY RADAR, WHICH
SHOULD CONTINUE FOR THE NEXT FEW HOURS.  LOCAL AMOUNTS UP TO 3"
ARE POSSIBLE.  SOILS ARE SATURATING IN THE AREA, WHICH ADDS TO THE
FLOODING RISK.  URBANIZED AREAS AND LOCATIONS WITH POOR DRAINAGE
ARE MOST AT RISK FOR ISSUES FROM HEAVY RAINFALL.

ROTH

ATTN...WFO...BGM...CTP...LWX...PHI...

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

LAT...LON   41877704 41687637 40827626 40347629 39437700
            39127734 39257778 40457800 41447760