MESOSCALE PRECIPITATION DISCUSSION 0258
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1021 AM EDT SAT JUN 02 2018

AREAS AFFECTED...PORTIONS OF WV AND VA

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

VALID 021421Z - 021900Z

SUMMARY...RAINFALL EXPECTED TO GRADUALLY INCREASE IN COVERAGE AND
INTENSITY INTO EARLY AFTERNOON ACROSS AREAS WITH ALREADY SATURATED
GROUND. FLASH FLOODING IS POSSIBLE.

DISCUSSION...AN AREA OF MODERATE TO OCCASIONALLY HEAVY RAINFALL IS
ONGOING ACROSS ERN WV THIS MORNING IN THE VICINITY OF A SURFACE
FRONT AND AHEAD OF AN APPROACHING UPPER-LEVEL VORT MAX. THE
ATMOSPHERE IS VERY MOIST ACROSS THE MID-ATLANTIC REGION, WITH
PWATS RANGING FROM 1.6-1.9 PER LATEST SPC MESOANALSYSIS AND
SUPPORTED BY 12Z IAD RAOB. INSTABILITY IS RELATIVELY WEAK AT THIS
TIME (MUCAPE OF 500-1000 J/KG AND MLCAPE LESS THAN 500 J/KG), BUT
12Z RAOB DATA REVEAL GOOD UPPER DIFFLUENT FLOW ACROSS THE REGION
WHICH IS LIKELY AIDING IN THE MAINTENANCE OF THE CURRENT ACTIVITY.
LATEST RAINFALL RATES IN THE ACTIVITY ACROSS ERN WV OF AROUND 0.50
IN/HR ARE INDICATED BY MESONET OBSERVATIONS, AND RADAR ESTIMATES
SEEM TO BE SIGNIFICANTLY UNDERDONE LIKELY DUE TO THE FAIRLY
SHALLOW NATURE OF THE CONVECTION AND DOMINANT WARM RAIN PROCESSES.
LATEST GOES-16 INFRARED DATA INDICATE A GRADUAL COOLING OF CLOUD
TOPS ACROSS WV SUGGESTING THAT RAIN RATES SHOULD BE ON A GRADUAL
INCREASE.

AS INSTABILITY INCREASES THROUGH LATE MORNING AND INTO EARLY
AFTERNOON (MLCAPE EXPECTED TO REACH INTO THE 500-1000 J/KG RANGE),
ALONG WITH A CONTINUATION OF FAVORABLE UPPER-LEVEL DYNAMICS AS THE
UPPER VORT MAX DRIFTS EASTWARD, WOULD EXPECT CONVECTION TO
INCREASE IN COVERAGE ACROSS WEST CENTRAL VA, AND THIS SCENARIO IS
DEPICTED BY THE LATEST HRRR/HRRR-EXP RUNS. ADDITIONALLY, A
CONTINUATION OR INCREASE IN ONGOING ACTIVITY ACROSS ERN WV IS
POSSIBLE FOR SEVERAL MORE HOURS WHILE UPPER DYNAMICS REMAIN
FAVORABLE. THE HRRR-TIME LAGGED ENSEMBLE SHOWS THE GREATEST
PROBABILITIES FOR >1 IN/HR RAIN RATES INITIALLY ACROSS ERN WV OVER
THE NEXT COUPLE HOURS, THEN SHOWS THEM MIGRATING SOUTHWARD INTO
WESTERN VA, WITH A POTENTIAL WANING OF RATES ACROSS WV AFTER ABOUT
17Z.

THE HRRR/HRRR-EXP BOTH SHOW SCATTERED RAINFALL AMOUNTS OF 1-3
INCHES ACROSS THE OUTLINED AREA THROUGH 19Z. GIVEN SATURATED
GROUND AND VERY LOW FFG, FLASH FLOODING IS POSSIBLE.

RYAN

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

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

LAT...LON   39617876 39287825 38887808 38227788 37597793
            37247830 37087895 37227975 37538049 38198093
            38798079 39308040 39488002 39607956