MESOSCALE PRECIPITATION DISCUSSION 0543
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
915 PM EDT FRI OCT 02 2015
 
AREAS AFFECTED...W VIRGINIA....E WEST VIRGINIA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 030114Z - 030714Z
 
SUMMARY...MOISTURE FLUX INTO OROGRAPHY TO PRODUCE POSSIBLE RATES
CAPABLE OF EXCEEDING FLASH FLOOD GUIDANCE.

DISCUSSION...LARGE SCALE ASCENT WILL CONTINUE TO INCREASE AS A
SUBTLE S/W LIFTS NORTH THROUGH INCREASING DIVERGENT UPPER LEVEL
FLOW ACROSS S CENT VA OVER THE NEXT FEW HOURS.  THIS WILL ALSO
SUPPORT INCRASING LOW LEVEL FLOW.  VWP OUT OF THE DC METRO SHOWS
STRONG 40 KT 85H FLOW OUT OF THE DUE EAST AT THE APEX OF THE SSW
TO NNE ORIENTED MST GRADIENT PER THE BLENDED TPW IMAGERY
REINFORCED BY GPS TPW NETWORK VALUES... 1.3" IN THE HIGHER TERRAIN
OF WV BACK TO NEAR 2.0" ALONG THE CHESAPEAKE BAY.  RAP AND HRRR
FORECASTS ARE FOR SLIGHTLY INCREASING 85H INTO THE NORTHERN
VIRGINIA HIGHER TERRAIN WHERE 1 HR FFG VALUES ARE .25-.75" AND 6HR
AS LOW A 1".  WITH THE AVAILABLE MST FLUX ON THIS INCREASING
EASTERLY FLOW...BROAD SCALE ASCENT COMPOUNDED BY OROGRAPHIC
ASCENT...RATES MAY BE LOW AOA .25"/HR BUT SUFFICIENT FOR FLOODING
CONDITIONS POSSIBLY FLASHY AT TIMES WITH ANY LOCALIZED ENHANCED
SHOWERS. THIS IS SUPPORTED BY THE RECENT ESRL EXPERIMENTAL
HRRR...NSSL-WRF AND TO A LESSER EXTENT RECENT OPERATIONAL HRRR
RUNS.  

AS THE S/W LIFTS NORTH ACROSS THE NC/VA LINE...LOW LEVEL FLOW IS
WEAKENED A BIT AND FLUX IS REDUCED WHICH LOWERS CONFIDENCE IN
PROLONGED STRONG FLOW ASCENDING ACROSS THE OROGRAPHY.  GIVEN
HIGHER GUIDANCE AS WELL AND LOWER HI-RES CAM QPF
SIGNAL...CONFIDENCE IN QPF/FLASH FLOODING IS LESSENED ACROSS W/SW
VIRGINA.  


GALLINA

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

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

LAT...LON   39417828 39327782 39197764 38897758 38477781 
            37917840 37467892 37267949 37448025 37928011 
            38957933 39227885