MESOSCALE PRECIPITATION DISCUSSION 0255
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
350 PM EDT SUN MAY 21 2017

AREAS AFFECTED...PIEDMONT OF SC & SOUTHWEST NC

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

VALID 211950Z - 212350Z

SUMMARY...A TRAINING BAND OF CONVECTION IS ATTEMPTING TO FORM
ACROSS SC AT THE PRESENT TIME.  HOURLY RAIN RATES TO 2" AND LOCAL
AMOUNTS TO 3" ARE POSSIBLE.

DISCUSSION...AN MCV FROM OVERNIGHT CONVECTION HAS DEVELOPED AN
OCCLUDED STRUCTURE IN THE THERMAL FIELD, WITH TEMPERATURES RISING
INTO THE MID TO UPPER 80S IN CENTRAL SC AND EAST-CENTRAL GA.  THIS
HAS CAUSED MLCAPES TO RISE TO 1000-2000 J/KG, WELL MORE THAN
FORECAST ON RECENT RAP RUNS.  INFLOW AT 850 HPA IS 25 KTS PER THE
COLUMBIA/CAE VAD WIND PROFILE.  EFFECTIVE BULK SHEAR OF 25-30 KTS
IS ENABLING THE CURRENT ATTEMPT AT A TRAINING BAND, ALONG WITH
FAIRLY UNIDIRECTIONAL SOUTHERLY FLOW FROM THE SURFACE TO 500 HPA. 
PRECIPITABLE WATER VALUES ARE ~2".

MLCAPES SHOULD RISE ANOTHER 500+ J/KG PRIOR TO SUNSET, WHICH
SHOULD ALLOW FOR GREATER COVERAGE AND INTENSITY TO CONVECTION
UNTIL AROUND 00Z.  THUNDERSTORMS WITH HEAVY RAIN SHOULD MAKE IT
INTO SOUTHWEST NC WITH TIME.  FLASH FLOOD GUIDANCE IS RATHER HIGH,
SO BELIEVE THE RISK FOR EXCESSIVE RAINFALL IS GREATEST IN URBAN
AREAS WITHIN THE SC AND NC PIEDMONT.  HOURLY RAIN RATES UP TO 2",
AND LOCAL AMOUNTS TO 3" ARE ANTICIPATED.  THE GUIDANCE SHOWS MORE
THAN THE USUAL VARIATION ON AMOUNTS HERE, SO THERE IS MORE
UNCERTAINTY THAN USUAL REGARDING THE MAGNITUDE OF HEAVY RAINFALL. 
BECAUSE OF THE HIGH FLASH FLOOD GUIDANCE AND GREATER UNCERTAINTY,
KEPT THE CATEGORY AS POSSIBLE FOR THE MPD.

ROTH

ATTN...WFO...CAE...GSP...RAH...

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

LAT...LON   35878060 35018025 33998059 33758169 34218252
            34678276 35518198