MESOSCALE PRECIPITATION DISCUSSION 0175
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
307 PM EDT TUE MAY 03 2016
 
AREAS AFFECTED...WESTERN VA....WESTERN AND CENTRAL NC 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 031900Z - 032300Z
 
SUMMARY...AN INCREASING AREA OF CONVECTION OVER THE HIGHER TERRAIN
OF WESTERN VA/NC COULD PRODUCE HEAVY RAINFALL IN AREAS WITH LOWER
FFG VALUES...RESULTING IN LOCALIZED FLASH FLOODING.

DISCUSSION...REGIONAL RADARS SHOWED AN INCREASING AREA OF
SCATTERED CONVECTION FORMING OVER AND IN THE LEE OF THE HIGHER
TERRAIN FROM WESTERN VA THROUGH WESTERN NC. CLEARING HAS ALLOWED
THE AIRMASS JUST EAST OF THE TERRAIN TO RECOVER WITH RESPECT TO
INSTABILITY...AS MLCAPE VALUES HAVE INCREASED TO BETWEEN 250 AND
500 J/KG...WITH THE HIGHEST VALUES ACROSS WESTERN NC. THE BEST
AXIS OF MOISTURE RESIDES CLOSER TO THE NC/SC COASTS...WITH
PRECIPITABLE WATER VALUES NEAR 1.20 INCHES COINCIDENT WITH THE
DEVELOPING INSTABILITY AXIS. 

THUS FAR...HOURLY RAINFALL RATES PER REGIONAL RADARS ARE GENERALLY
LESS THAN AN INCH (WITH HIGHER RATES CLOSER TO AN INCH WESTERN NC.
HIGH RESOLUTION MODELS... INCLUDING THE LATEST HRRR...12Z SPC WRF
AND 12Z WRF ARW...SUGGEST THAT THE CONVECTION COULD BECOME BETTER
ORGANIZED AS IT LEAVES THE HIGHER TERRAIN (AS THE CONVECTION
ENCOUNTERS 45 TO 55 KNOTS OF EFFECTIVE SHEAR. THE ORGANIZING
CONVECTION...MOVING INTO BETTER MOISTURE... COULD RESULT IN HOURLY
RAINFALL RATES OF BETTER THAN AN INCH. THESE RATES ARE SUPPORTED
BY THE LATEST HRRR.

FLASH FLOOD GUIDANCE VALUES ARE LOWER THAN AN INCH ACROSS PORTIONS
OF WESTERN VA...WHERE SOME OF THE CAM GUIDANCE SUGGESTS LOCAL 1-2
INCH RAINFALL AMOUNTS THROUGH LATE AFTERNOON. FURTHER SOUTH...THE
FLASH FLOOD GUIDANCE VALUES ARE HIGHER...BUT REGIONAL RADARS
INDICATED BETWEEN 3 AND 5 INCHES OF RAINFALL IN THE LAST 24 HOURS
ACROSS PORTIONS OF WESTERN NC...ESPECIALLY IN THE VICINITY OF KCLT.

IN GENERAL...THE OVERALL FLASH FLOOD THREAT SHOULD BE LOCALIZED.
HOWEVER... GIVEN HEAVY RAINFALL DURING THE PAST 24 HOURS...ANY
ADDITIONAL CONVECTION COULD RESULT IN FLASH FLOODING.

HAYES

ATTN...WFO...AKQ...CAE...GSP...LWX...MRX...RAH...RNK...

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

LAT...LON   39007853 38837733 36207893 36027898 35437945 
            34998031 34898098 35068187 35308231 35428244 
            35438246 36498162 37638009