MESOSCALE PRECIPITATION DISCUSSION 0692
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1113 AM EST THU DEC 24 2015
 
AREAS AFFECTED...S-CNTRL VIRGINIA TO THE DELMARVA PENINSULA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 241613Z - 242200Z
 
SUMMARY...TRAINING RAINS AND A FLASH FLOOD THREAT WILL PERSIST
OVER CNTRL VIRGINIA...EXTENDING TO THE DELMARVA PENINSULA INTO THE
AFTERNOON. HOURLY RATES OF 1 TO 1.5 IN/HR WILL BE POSSIBLE WITH 6
HOUR TOTALS UP TO 3 INCHES POSSIBLE THROUGH 22Z. 

DISCUSSION...MORNING RAOBS AND GPS SITES SHOWED PRECIPITALBE WATER
VALUES OF 1.5 TO 1.7 INCHES FROM THE NORTH CAROLINA/VIRGINIA
BORDER TO THE DELMARVA PENINSULA WHICH ARE RECORD OR NEAR RECORD
VALUES FOR THE MONTH OF DECEMBER. 850-700 MB FLOW OF 50-60 KTS
ACROSS VIRGINIA PER RECENT VAD WIND PLOTS IS TRANSPORTING DEEP
MOISTURE FROM THE SOUTHEAST U.S. INTO THE MID-ATLANTIC REGION. THE
CIRA LAYERED PRECIPITABLE WATER PRODUCT SHOWS THAT THE PLUME OF
MOISTURE HAS A DIRECT CONNECTION TO THE TROPICAL EAST PACIFIC IN
THE MID-UPPER LEVELS...OFTEN PRESENT DURING SIGNFICANT FLASH FLOOD
EVENTS. 

CONFLUENT FLOW WAS NOTED AT 850 MB ACROSS THE MPD THREAT AREA AND
BROAD DIFFLUENCE WAS NOTED ALOFT...TO THE SOUTHEAST OF A 170+ KT
JET CORE LOCATED OVER PARTS OF THE MIDWEST. WHILE RECENT RUNS OF
THE RAP HAVE BEEN UNDERDOING THE MAGNITUDE OF THE LOW LEVEL FLOW
BY UP TO 10 KTS...THE RAP FORECASTS THE GREATEST 850-700 MB
MOISTURE TO STREAM NEWD ACROSS CNTRL AND SRN VIRGINIA INTO THE
AFTERNOON WITH PERHAPS A SLIGHT WEAKENING OF LOW LEVEL FLOW.
VISIBLE SATELLITE IMAGERY HAD INDICATED A FEW BREAKS IN OTHERWISE
THICK CLOUD COVER OVER SERN VIRGINIA WHICH SHOULD HELP TO MAXIMIZE
INSTABILITY ACROSS SRN PORTIONS OF VIRGINIA INTO THE AFTERNOON.
GIVEN THE UNIDIRECTIONAL FLOW AND ANOMALOUS MOISTURE IN
PLACE...TRAINING OF HEAVY RAIN WITH HOURLY RAIN RATES OF 1 TO 1.5
IN/HR APPEAR LIKELY THROUGH THE AFTERNOON. WITH FLASH FLOOD
GUIDANCE AS LOW AS 0.5 IN/HR AND 1.0 IN/3 HRS...FLASH FLOODING IS
EXPECTED ACROSS THE REGION THROUGH THE AFTERNOON.

OTTO

ATTN...WFO...AKQ...LWX...PHI...RAH...RNK...

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

LAT...LON   38957509 38047523 36907763 36147954 36068069 
            36998052 37747933 38417731 38817609