MESOSCALE PRECIPITATION DISCUSSION 0519
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
121 AM EDT MON JUL 23 2018

AREAS AFFECTED...DC METRO AREA INTO SOUTHERN PA

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

VALID 230520Z - 230820Z

SUMMARY...CELL COVERAGE IS INCREASING OVER AN AREA OF SATURATED
SOILS.  HOURLY RAIN RATES UP TO 1.5" WITH LOCAL AMOUNTS OF 3"
COULD LEAD TO ISSUES.

DISCUSSION...SHOWERS AND THUNDERSTORMS ARE INCREASING IN COVERAGE
FROM CENTRAL MD INTO SOUTHERN PA NORTH OF A VAGUE THERMAL BOUNDARY
ACROSS SOUTHERN MD.  THIS APPEARS TO BE OCCURRING IN ADVANCE OF A
CONVECTIVELY-FED SHORTWAVE ACROSS SOUTHWEST VA.  HOURLY RAIN
TOTALS ARE BEGINNING TO EXCEED 1".  MU CAPES OF 500-1500 J/KG LIE
ACROSS THE REGION.  IN ADDITION TO THE SATURATED SOILS, THE
ATMOSPHERE IS ALSO SATURATED WITH PRECIPITABLE WATER VALUES OF
1.75-2" PER GPS DATA.  INFLOW AT 850 HPA OFF THE INSTABILITY POOL
ACROSS SOUTHERN MD IS SOUTHERLY AT 25-30 KTS.  EFFECTIVE BULK
SHEAR COMBINED WITH UNIDIRECTIONAL FLOW WITH HEIGHT ARE TRYING TO
ORGANIZE THE SHOWERS AND THUNDERSTORMS INTO A NORTH-SOUTH BAND.

SOME OF THE GUIDANCE HAS A CONCEPT OF WHAT IS OCCURRING AT THIS
TIME, PARTICULARLY THE 00Z ARW AND 00Z NMMB GUIDANCE.  CONSIDERING
CURRENT RADAR TRENDS, HOURLY RAIN TOTALS TO 1.5" WITH LOCAL
AMOUNTS TO 3" ARE ANTICIPATED.  THIS WOULD BE PROBLEMATIC IN URBAN
AREAS AND OVER SATURATED SOILS.

ROTH

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

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

LAT...LON   41137672 40127608 39037658 38577754 39447793
            40737785