MESOSCALE PRECIPITATION DISCUSSION 0884
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
524 PM EDT WED OCT 11 2017

AREAS AFFECTED...SERN VA

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

VALID 112123Z - 120300Z

SUMMARY...THERE WILL BE POTENTIAL FOR LOCALLY HEAVY RAINFALL AND
FLASH FLOODING OVER PORTIONS OF SERN VA THIS EVENING WITH RAINFALL
RATES OF 2-3 IN/HR. STORM TOTAL RAINFALL OF 4-6 INCHES IS EXPECTED
THROUGH 03Z.

DISCUSSION...KAKQ REFLECTIVITY AT 21Z SHOWED A FEW SLOW MOVING
CORES OF CONVECTION OVER SERN VA...GENERALLY MOVING TOWARD THE
EAST AT 10 KT. HOWEVER...CELLS OVER SRN SUSSEX COUNTY AND THE
PENINSULA WERE BACK BUILDING WITH DUAL POL RAINFALL RATES OF
1.5-2.0 IN/HR. GPS PRECIPITABLE WATER VALUES WERE 2.2-2.3 INCHES
TO THE EAST OF I-95 AND NEAR/SOUTH OF A STATIONARY FRONT WHICH
CROSSED FROM EAST TO WEST JUST NORTH OF ORF AT 21Z. MLCAPE VALUES
ARE MAXIMIZED ALONG AND SOUTH OF THE STATIONARY FRONT WHICH SHOULD
SUPPORT HEAVY RAINFALL RATES GIVEN THE HIGHLY ANOMALOUS MOISTURE
IN PLACE.

TRAINING RAINFALL IS EXPECTED TO CONTINUE WITH SIMILAR LOW LEVEL
WINDS OF ABOUT 15 KT VIA KAKQ VAD WIND DATA AT 850 MB TO MEAN CELL
MOTIONS. FLOW ALOFT IS SLIGHTLY DIFFLUENT WHICH MAY HELP TO
ENHANCE VERTICAL MOTIONS...SIMILAR TO CONVECTION THAT OCCURRED
TUESDAY NIGHT OVER CNTRL VA. WHILE CELL COVERAGE SHOULD BE LIMITED
AND ANTECEDENT CONDITIONS ARE RATHER DRY...SOME FLASH FLOODING
COULD OCCUR WITH RAINFALL RATES OF 2-3 IN/HR...ESPECIALLY OVER
URBAN LOCATIONS. RAP FORECASTS SHOW WLY 850 MB FLOW LOWERING
PRECIPITABLE WATER VALUES GRADUALLY THROUGH 03Z AHEAD OF AN
APPROACHING COLD FRONT. ANY LINGERING CONVECTION IS EXPECTED TO
DIMINISH BEYOND 01-02Z WITH THE LOSS OF DAYTIME HEATING AND
LOWERING PRECIPITABLE WATER VALUES...BUT TRENDS WILL BE MONITORED
THROUGH 03Z AND ANOTHER MPD COULD BE NEEDED IF IT APPEARS
CONVECTION WILL PERSIST LONGER THAN CURRENTLY EXPECTED.

OTTO

ATTN...WFO...AKQ...

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

LAT...LON   37897576 37457439 36677446 36387574 36527745
            37317793 37667710