MESOSCALE PRECIPITATION DISCUSSION 0259
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
222 PM EDT SAT JUN 02 2018

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

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 021821Z - 022300Z

SUMMARY...HEAVY RAINFALL PRODUCING SHOWERS AND THUNDERSTORMS ARE
EXPECTED TO INCREASE IN COVERAGE INTO EARLY EVENING. WITH GROUND
ALREADY SATURATED IN MANY AREAS DUE TO RECENT RAINS, FLASH
FLOODING IS LIKELY.

DISCUSSION...MULTIPLE FACTORS ARE SUPPORTIVE OF HEAVY RAINFALL
ACROSS PORTIONS OF THE MID-ATLANTIC REGION THIS AFTERNOON. A POOL
OF DEEP AND ANOMALOUS MOISTURE (PWATS AROUND 2 INCHES) IS IN PLACE
EAST OF THE CENTRAL APPALACHIANS. THESE VALUES ARE NEAR 3 STANDARD
DEVIATIONS ABOVE AVERAGE, AND ARE AT OR SURPASSING THE 99TH
PERCENTILE BASED ON ESAT DATA. TWO MID-UPPER LEVEL VORTICITY
MAXIMA ARE NOTED ON GOES-16 WATER VAPOR IMAGERY ACROSS THE REGION
THIS AFTERNOON, ONE CROSSING WEST VIRGINIA THIS AFTERNOON,
ASSOCIATED WITH A BROADER UPPER TROUGH, AND A SECOND MORE SUBTLE
FEATURE NOTED ACROSS NORTHERN NORTH CAROLINA MOVING NORTHEASTWARD.
ADDITIONALLY, A LOW-LEVEL CIRCULATION WAS NOTED ON VISIBLE
SATELLITE, AND ALSO ON THE LATEST SPC MESOANALYSIS ACROSS EAST
CENTRAL VA, RESULTING IN A REGION OF ENHANCED LOW-LEVEL
CONVERGENCE ACROSS CENTRAL VA. INSTABILITY HAS INCREASED THROUGH
THE DAY, AND MUCAPE VALUES HAVE REACHED 1000-2000 J/KG ACROSS THE
AREA.

CONVECTIVE ACTIVITY SHOULD CONTINUE TO INCREASE THROUGH THE NEXT
SEVERAL HOURS AS THE UPPER-LEVEL DISTURBANCES APPROACH THE AREA OF
CONCERN. HI-RES GUIDANCE SHOW SOME DISCREPANCIES AS TO PLACEMENT
OF THE HIGHEST RAINFALL AMOUNTS. BUT IN GENERAL, WOULD EXPECT
GREATEST CONCENTRATION OF THUNDERSTORMS INITIALLY ACROSS
WEST-CENTRAL VA, WITH ACTIVITY GRADUALLY SPREADING NORTH/EAST
THROUGH LATE AFTERNOON/EARLY EVENING ALONG WITH THE BEST
UPPER-LEVEL FORCING. THE HRRR SEEMED TO HAVE A GOOD HANDLE ON THE
ONGOING CONVECTION, AND THE 12Z WRF-ARW IS SIMILAR. BOTH OF THESE
SOLUTIONS HIGHLIGHT AREAS ACROSS CENTRAL VA WITH THE GREATEST
THREAT FOR HEAVY RAINFALL OVER THE NEXT SEVERAL HOURS, WITH THE
POSSIBILITY FOR ADDITIONAL AREAS OF HEAVY RAIN IN CLOSER PROXIMITY
TO THE SURFACE FRONT OVER NORTHERN VA/MD. THE HRRR AND ARW
INDICATE THAT LOCALIZED AMOUNTS EXCEEDING 3 INCHES (AND HOUR RATES
OF 1-1.5 INCHES) ARE POSSIBLE THROUGH 00Z. GIVEN GROUND ALREADY
SATURATED IN MANY AREAS FROM RECENT RAINS, FLASH FLOODING IS
LIKELY.

RYAN

ATTN...WFO...AKQ...LWX...PBZ...PHI...RLX...RNK...

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

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            37347650 37007700 36987788 37257876 37697941
            38007979 38648010 39117999 39467948 39527861
            39497786 39607732