MESOSCALE PRECIPITATION DISCUSSION 0341
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1148 PM EDT FRI JUL 10 2015
 
AREAS AFFECTED...WEST VIRGINIA...NORTHERN VIRGINIA...SOUTHERN
MARYLAND...DISTRICT OF COLUMBIA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 110347Z - 110947Z
 
SUMMARY...SHORT TERM ISOLATED FLASH FLOOD THREAT WITH TRAINING OF
MODERATE CELLS...EVENTUALLY INCREASING IN COVERAGE AND INTENSITY
BY 06Z.

DISCUSSION...WV LOOP INDICATES WELL DEFINED SHORTWAVE ACROSS
EASTERN OHIO BEGINNING TO DROP SOUTHEAST WITH CONVECTION STARTING
TO GROW IN STRENGTH ALONG THE INFLECTION POINT OF THE SHORTWAVE
THAT COLLOCATES WITH THE INTERSECTION OF A WEST-EAST ORIENTED
SURFACE FRONT.  RAP ANALYSIS SHOWS A NARROW INSTABILITY AXIS OF
500-1000 J/KG MUCAPES AVAILABLE FROM THE FRONT SOUTH. DEEP
MOISTURE IS POOLING ALONG THE FRONT WITH TPW ANALYSIS PER GPS
NETWORK AND RAOBS IN THE 1.8" RANGE. WITH LESS THAN 1000 FT
DIFFERENCES BETWEEN WET BULB ZERO AND FREEZING LEVEL IN THE
SURROUNDING 00Z ILN/IAD SOUNDING THAT RAINFALL EFFICIENCY WILL BE
HIGH.  NEARLY UNIDIRECTIONAL FLOW THROUGH THE CLOUD BEARING LAYER
WILL SUPPORT TRAINING ALONG THE FRONT...AND SOME INDICATIONS OF
ENOUGH UPSTREAM ENERGY FOR SOME SLIGHT  BACKBUILDING IN THE SHORT
TERM.   SOME INDICATIONS PER 30-35KTS OF EFFECTIVE SHEAR FOR SOME
WEAK SUPERCELLULAR NATURE ALONG THE FRONT SHOULD SUPPORT SLIGHT
RIGHT TURNING AND SLOWING OF FORWARD PROPAGATION FOR INCREASING
TOTALS AS WELL.  

HI-RES MODELS DO INDICATE SOME REDUCTION OF THE INSTABILITY
THROUGH WEST VIRGINIA IN THE EARLY MORNING HOURS...BUT HIGH
AMOUNTS REMAIN EAST OF THE HIGHER TERRAIN IN NORTHERN
VIRGINIA/MARYLAND WITH INCREASING SOUTHERLY LOW LEVEL FLOW WITH
THE WEAK HEIGHT FALLS...THIS SHOULD CONTINUE TO NARROW AND FOCUS
INCREASINGLY STRONGER CONVECTION AND HIGHER RATES TOWARD THE END
OF THE DISCUSSION PERIOD NEAR 8-10Z.  HI-RES MODEL AGREEMENT HAS
INCREASED WITH THE RECENT RUNS OF THE HRRR AND NEW 00Z
NAM-CONEST...SUPPORTING THE IDEA OF 1-3" TOTALS ACROSS WV WITH
INCREASING 2-4" NEARER THE FRONT ACROSS CENTRAL WV INTO NORTHERN
VIRGINIA.  GIVEN ANTECEDENT CONDITIONS FLASH FLOODING IS LIKELY. 

GALLINA

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

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

LAT...LON   39307937 39147761 38727603 37987622 37397808 
            37688166 38448252 38908195 39298123