MESOSCALE PRECIPITATION DISCUSSION 0263
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1057 AM EDT SUN JUN 03 2018

AREAS AFFECTED...NORTHERN AND AND EAST CENTRAL VA...DC...MD AND DE

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

VALID 031456Z - 032000Z

SUMMARY...THE COMBINATION OF DEEP TROPICAL MOISTURE, A SURFACE
FRONTAL BOUNDARY, AND A LOW-LEVEL CIRCULATION WILL SUPPORT
LOCALIZED AREAS OF FLASH FLOODING INTO THE AFTERNOON ACROSS
PORTIONS OF THE MID-ATLANTIC REGION.

DISCUSSION...A FRONTAL BOUNDARY AS SLOWLY PRESSED SOUTHWARD ACROSS
THE MID-ATLANTIC REGION, USHERING IN A SLIGHTLY DRIER AIR AT THE
LOW-LEVELS (AS EVIDENCED BY SURFACE DEW POINTS DROPPING INTO TO
NEAR 60 AT SOME LOCATIONS NORTH OF THE FRONT). THE ATMOSPHERE
REMAINS VERY MOIST OVERALL, HOWEVER, WITH PWATS APPROACHING 2
INCHES. A PERSISTENT LOW-LEVEL CIRCULATION IS LOCATED JUST NORTH
OF RICHMOND, VA AND APPEARS NEARLY STATIONARY ON LATEST GOES-16
VIS IMAGERY (AFTER DRIFTING NORTHWEST OVER THE PAST SEVERAL
HOURS). MODEST INSTABILITY REMAINS IN THE INFLOW REGION SOUTH/EAST
OF THE LOW, WITH MLCAPES AROUND 500 J/KG PER LATEST SPC
MESOANALYSIS. A PERSISTENT AREA OF CONVECTION WAS ONGOING NEAR THE
CIRCULATION CENTER, WITH OBSERVED RAINFALL RATES APPROACHING 2
IN/HR OVER THE PAST COUPLE HOURS. LATEST IR IMAGERY SHOW A VERY
SLOW WARMING OF CLOUD TOPS NEAR THE CIRCULATION, SUGGESTING THAT
THE POTENTIAL FOR 2 IN/HR RAINFALL RATES MAY BE WANING A BIT.

FARTHER NORTH, THE COMBINATION OF FLOW AROUND THE LOW-LEVEL
CIRCULATION AND HIGHER PRESSURE NOSING IN FROM THE NORTHEAST NORTH
OF THE FRONT WAS ENHANCING LOW-LEVEL EASTERLY FLOW NORTH OF THE
FRONT FROM THE WV PANHANDLE EAST TO DE AND SOUTHERN NJ, INCREASING
THE POTENTIAL FOR SOME UPSLOPE ENHANCEMENT OF RAINFALL. AN AREA OF
SHOWERS/THUNDERSTORMS WAS ONGOING FROM NEAR THE CHESAPEAKE EAST
ACROSS THE DELMARVA PENINSULA TO THE ATLANTIC.

HI-RES MODELS HAVE STRUGGLED TO GRASP THE ONGOING SCENARIO, EITHER
NOT DEPICTING THE LOW-LEVEL CIRCULATION WELL OR SHOWING IT TOO FAR
SOUTH. THE HRRR-EXPERIMENTAL SEEMED TO BE THE CLOSEST SOLUTION TO
REALITY. THE HRRR-EXP SHOWS THE CIRCULATION REMAINING NEARLY
STATIONARY THROUGH EARLY AFTERNOON BEFORE GRADUALLY BEGINNING A
SLOW MOVEMENT EASTWARD, LIKELY IN RESPONSE TO HEIGHT FALLS
PROGRESSING ACROSS THE OH VALLEY. THE HRRR-EXP SUGGESTS THE
POTENTIAL FOR CONTINUED HEAVY RAINS IN CLOSE PROXIMITY TO THE
CIRCULATION, WITH THE POTENTIAL FOR ADDITIONAL HEAVY RAINS FARTHER
NORTH ACROSS NORTHERN VA AND PORTIONS OF MD IN A DEFORMATION BAND,
LIKELY WITH SOME UPSLOPE AND ISENTROPIC ENHANCEMENT AS WELL. BASED
ON THIS SOLUTION ADDITIONAL RAINFALL AMOUNTS OF 1-3 INCHES APPEAR
POSSIBLE THROUGH 20Z, WITH RATES OF 1-2 IN/HR POSSIBLE AT TIMES,
ESPECIALLY NEAR THE CIRCULATION. GIVEN SATURATED GROUND DUE TO
RECENT HEAVY RAINS, FLASH FLOODING IS POSSIBLE.

RYAN

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

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

LAT...LON   39687668 39607609 39417571 38937537 38457520
            37877553 37447604 37197645 37097693 37287743
            37767820 38397837 39147804 39547747