MESOSCALE PRECIPITATION DISCUSSION 0522
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
727 AM EDT MON JUL 23 2018

AREAS AFFECTED...CENTRAL PA...NORTHERN MD...DC...NORTHERN VA...WV
PANHANDLE

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

VALID 231126Z - 231500Z

SUMMARY...THUNDERSTORMS IN THE VICINITY OF A SURFACE FRONTAL
BOUNDARY COULD RESULT IN LOCALIZED AREAS OF FLASH FLOODING.

DISCUSSION...SOUTHERLY FLOW EAST OF A MID/UPPER-LEVEL LOW CENTERED
OVER THE OHIO VALLEY IS TRANSPORTING DEEP TROPICAL MOISTURE
NORTHWARD ALONG THE EASTERN SEABOARD INTO THE MID-ATLANTIC REGION,
WITH PW VALUES IN THE 1.7-1.9 INCH RANGE PER LATEST SPC
MESOANALYSIS. DESPITE RATHER RAPID FORWARD MOVEMENT OF CONVECTIVE
CELLS (NORTHWARD AT 25-30 KT), HIGH PRECIPITATION EFFICIENCY WAS
RESULTING IN RADAR ESTIMATED RAINFALL RATES OF 0.5-1.0 IN/HR IN
THE VICINITY OF A SURFACE FRONTAL BOUNDARY. SUFFICIENT INSTABILITY
(MUCAPE OF 1000-2000 J/KG) ALONG WITH UPPER DIVERGENCE ON THE
SOUTHERN PERIPHERY OF AN UPPER-LEVEL SPEED MAX SHOULD PROVIDE
SUPPORT FOR MAINTENANCE OF CONVECTION THROUGH THE NEXT FEW HOURS.

MANY OF THE LATEST CAM RUNS DO NOT SEEM TO HAVE A GOOD HANDLE OF
THE ONGOING CONVECTION, ALTHOUGH THE HRRR AND NAM-CONEST DO
SUGGEST THE POTENTIAL FOR LOCALIZED RAINFALL AMOUNTS OF 1-3 INCHES
OVER THE NEXT SEVERAL HOURS. THIS WOULD PRIMARILY BE DUE TO ANY
AREAS OF POTENTIAL CELL TRAINING THAT ARE ABLE TO SET UP. GIVEN
VERY LOW FLASH FLOOD GUIDANCE IN THE OUTLINED AREA (AS LOW AS 0.50
IN/HR IN SOME CASES), FLASH FLOODING IS POSSIBLE.

RYAN

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

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

LAT...LON   41377713 41057637 40267607 39117655 38827717
            38977770 39347824 40447836 41077799