MESOSCALE PRECIPITATION DISCUSSION 0158
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
253 PM EDT THU MAY 17 2018

AREAS AFFECTED...ERN WV INTO CNTRL VA

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

VALID 171853Z - 180050Z

SUMMARY...SLOW MOVING AND TRAINING CONVECTION IS EXPECTED TO
PRODUCE 2-4 INCHES OVER A 1-3 HOUR PERIOD THROUGH 01Z...EXTENDING
FROM EASTERN WEST VIRGINIA INTO CENTRAL VIRGINIA. GIVEN AREA WIDE
LOWERED FLASH FLOOD GUIDANCE...FLASH FLOODING WILL BE POSSIBLE.

DISCUSSION...VISIBLE SATELLITE IMAGERY OVER THE PAST HOUR HAS
SHOWED SCATTERED CONVECTION DEVELOPING SOUTH OF A STATIONARY FRONT
EXTENDING WEST TO EAST ACROSS CENTRAL VIRGINIA. THE FRONTAL
BOUNDARY SHOWS UP RATHER WELL IN VISIBLE IMAGERY WITH OVERCAST
CONDITIONS TO THE NORTH OF THE FRONT WHILE SCATTERED CLOUD COVER
TO THE SOUTH IS PRESENT...WHICH HAS ALLOWED THE DEVELOPMENT OF
WEAK MLCAPE...GENERALLY LESS THAN 1000 J/KG VIA THE LATEST SPC
MESOANALYSIS PAGE. SATELLITE IMAGERY AND REGIONAL RADAR ALSO
DEPICTED TWO SMALL MESOSCALE CIRCULATIONS...ONE OVER NORTHERN
NORTH CAROLINA AND THE OTHER OVER NORTHEASTERN SOUTH
CAROLINA...BOTH MOVING TOWARD THE NORTH-NORTHEAST. MOISTURE ACROSS
THE REGION IS PLENTIFUL WITH 12Z RAOBS DEPICTING PRECIPITABLE
WATER VALUES IN THE 90-95TH PERCENTILE AREA-WIDE.

INDIVIDUAL CELL MOTIONS HAVE BEEN TOWARD THE NORTH-NORTHEAST AT A
SLOW 5-15 KT...WHILE VAD WIND PROFILES HAVE DEPICTED 850 MB WINDS
OF A SIMILAR DIRECTION BETWEEN 10-15 KT. SOME BACKING OF 850 MB
FLOW IS EXPECTED OVER THE NEXT 3-6 HOURS VIA SHORT TERM RAP
FORECASTS AND LOCAL ENHANCEMENT TO 850 MOISTURE TRANSPORT CAN BE
EXPECTED AS THE MESOSCALE CIRCULATION NEAR THE VIRGINIA/NORTH
CAROLINA BORDER MOVES NORTH INTO THE EVENING.

IN THE VICINITY OF THE SURFACE BOUNDARY...ACTING AS A SOURCE OF
LOW LEVEL CONVERGENCE ALONG WITH LOCALLY PRODUCED OUTFLOW
BOUNDARIES...WILL LIKELY HELP TO SUSTAIN SLOW MOVING CONVECTION
INTO THE EARLY EVENING HOURS. GIVEN LOW FLASH FLOOD GUIDANCE
VALUES...ESPECIALLY IN THE VICINITY OF THE WEST VIRGINIA/VIRGINIA
BORDER...AND THE POTENTIAL FOR RAIN RATES OVER 2 IN/HR...A QUICK 2
TO 4 INCHES WILL BE POSSIBLE WHICH MAY LEAD TO SCATTERED FLASH
FLOODING ACROSS THE MPD THREAT AREA.

OTTO

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

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

LAT...LON   38437640 37877608 37377697 37047843 37228004
            37248112 37548128 38028081 38297979 38387792