MESOSCALE PRECIPITATION DISCUSSION 0264
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
354 PM EDT SUN JUN 03 2018

AREAS AFFECTED...PORTIONS OF VA...MD...DC AND DE

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

VALID 031954Z - 040000Z

SUMMARY...DEFORMATION BAND OF MODERATE TO HEAVY RAIN SHOULD
PERSIST FOR AT LEAST A FEW MORE HOURS BEFORE LIKELY
WEAKENING/DISSIPATING. FLOODING AND FLASH FLOODING WILL REMAIN A
POSSIBILITY INTO EARLY EVENING.

DISCUSSION...AN AREA OF LOW PRESSURE ACROSS SOUTHEASTERN VA HAS
BEEN NEARLY STATIONARY THROUGH THE DAY, BUT IS EXPECTED TO BEGIN
AN EAST-NORTHEASTWARD MOTION OVER THE NEXT SEVERAL HOURS. NORTH OF
THE LOW, A PERSISTENT DEFORMATION BAND HAS PRODUCED MODERATE TO
HEAVY RAIN ACROSS PORTIONS OF VA AND MD THROUGHOUT THE DAY.
INSTABILITY REMAINS RELATIVELY LIMITED, WITH MLCAPE IN THE 500 TO
1000 J/KG RANGE AHEAD OF THE SURFACE LOW/FRONT AND LITTLE TO NO
INSTABILITY IN THE COLD SECTOR NORTH OF THE FRONT. PWATS REMAIN
HIGH, HOWEVER (1.7-1.9 INCHES), AND DYNAMICAL FORCING ALONG WITH
ISENTROPIC LIFTING AND UPSLOPE ENHANCEMENT HAVE MANAGED TO PRODUCE
HEAVY RAIN DESPITE THE LACK OF INSTABILITY. LOCALIZED RAINFALL
RATES AS HIGH AS 2 IN/HR HAVE BEEN REPORTED OCCASIONALLY
THROUGHOUT THE DAY IN THE HEAVIEST SHOWERS. 

LATEST RADAR AND SATELLITE IMAGERY INDICATE THAT THIS DEFORMATION
BAND IS BEGINNING TO CONTRACT, AND THE HI-RES GUIDANCE ARE IN
GENERAL AGREEMENT THAT THE BAND SHOULD QUICKLY BEGIN TO WEAKEN
OVER THE NEXT FEW HOURS. THE HRRR/HRRR-EXP ARE THE QUICKEST WITH
THIS PROCESS, BRINGING AN END TO MOST RAIN IN THE DEFORMATION BAND
WITHIN THE NEXT 1-2 HOURS, WHILE THE WRF-ARW/NMM SHOW THIS
OCCURRING OVER A SEEMINGLY MORE REASONABLE 3-4 HOUR TIME PERIOD.
THE ARW/NMM SUGGEST THAT ANOTHER 1-2 INCHES OF ADDITIONAL RAINFALL
ARE POSSIBLE THROUGH THE NEXT SEVERAL HOURS. LOCALIZED FLOODING OR
FLASH FLOODING WILL REMAIN POSSIBLE THROUGH 00Z.

RYAN

ATTN...WFO...AKQ...LWX...PHI...

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

LAT...LON   39707648 39557563 39147537 38227591 37717614
            37397691 37597749 38257775 38977773 39487744
            39637699