MESOSCALE PRECIPITATION DISCUSSION 0504
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
714 AM EDT TUE JUL 18 2017

AREAS AFFECTED...NORTHEAST SC & SOUTHEAST NC

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

VALID 181114Z - 181459Z

SUMMARY...THUNDERSTORMS ARE SLOWLY INCREASING IN COVERAGE AND
SHOWING OCCASIONAL TRAINING CHARACTER.  HOURLY RAIN RATES UP TO
2.5" WITH LOCAL AMOUNTS UP TO 5" ARE POSSIBLE.

DISCUSSION...WATER VAPOR IMAGERY SHOWS A MID TO UPPER LEVEL LOW
NEAR THE NC/VA BORDER, WHICH IS FOSTERING UPPER LEVEL DIVERGENCE
OVER AN AREA OF THUNDERSTORMS WHICH HAS BEEN DISPLAYING COOLING
CLOUD TOPS AND HAS BEEN SLOWLY GROWING IN COVERAGE SINCE 07Z.  THE
CONVECTION IS ELEVATED OVER THE TOP OF THE SURFACE BOUNDARY
LOCATED VERY NEAR THE NC COAST AND JUST EAST OF A WEAK SURFACE
LOW.  PRECIPITABLE WATER VALUES ARE ~2" PER GPS DATA.  INFLOW AT
850 HPA IS SOUTHWEST AT 15-20 KTS PER VAD WIND PROFILES IN THE
REGION.  SPC MESOANALYSES INDICATE 25+ KTS OF EFFECTIVE BULK SHEAR
WHICH APPEARS TO BE TRYING TO ORGANIZE THE ACTIVITY INTO SHORT
TRAINING BANDS.  MUCAPE VALUES IN THE REGION ARE 1000-2000 J/KG.

THE 06Z SSEO NEIGHBORHOOD PROBABILITIES ADVERTISED THE CONVECTIVE
UPTICK RATHER WELL, ALTHOUGH A COUPLE HOURS DELAYED COMPARED TO
RADAR/SATELLITE TRENDS.  WHILE THE 09Z HRRR HAS THE INDICATION OF
A HIGHLY LOCALIZED MAXIMUM, THE 06Z CANADIAN REGIONAL (ALTHOUGH
SLIGHTLY TOO FAR TO THE NORTH) SHOWED A SPOT MAXIMUM TOWARDS 5" IN
SOUTHEAST NC THROUGH 15Z, WHICH SEEMS PLAUSIBLE.  THE AVAILABLE
MOISTURE AND INSTABILITY INDICATE THAT HOURLY RAIN RATES UP TO
2.5" ARE POSSIBLE.  SOME SLIGHT VEERING IN THE 850 HPA WIND WITH
TIME SUGGESTS THAT THE CONVECTION WILL EVENTUALLY PROGRESS
EASTWARD, WITH FORWARD PROPAGATING CONVECTIVE VECTORS SUGGESTING
SPEEDS UP TO 30 KTS.

ROTH

ATTN...WFO...CAE...ILM...MHX...RAH...

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

LAT...LON   35537687 35417539 34537643 33947814 34048013
            34108033 34877884