MESOSCALE PRECIPITATION DISCUSSION 0215...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1209 PM EDT FRI MAY 12 2017

CORRECTED FOR LAST SENTENCE

AREAS AFFECTED...SOUTHWEST VA & WV, NORTHEAST TN, & EASTERN KY

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

VALID 121605Z - 122205Z

SUMMARY...CONVECTION IS EXPECTED TO FORM IN THE AREA DURING THE
NEXT COUPLE HOURS AHEAD OF AN INCOMING MCV.  HOURLY RAIN RATES UP
TO 1", WITH LOCAL AMOUNTS UP TO 2", COULD LEAD TO FLOOD ISSUES
OVER SATURATED SOILS.

DISCUSSION...WATER VAPOR IMAGERY SHOWS AN MCV MOVING ACROSS
SOUTH-CENTRAL KY WHICH IS BEGINNING TO ENHANCE RADAR REFLECTIVITY
VALUES ACROSS EASTERN KY.  CIN STILL EXISTS NEAR A FRONTAL WAVE
ACROSS EASTERN KY, WITH MUCAPE OF 500-1000 J/KG FROM SOUTHERNMOST
WV INTO NORTHEASTERNMOST TN.  RECENT RADAR IMAGERY SUGGESTS CIN IS
IN THE PROCESS OF ERODING NOW, AS NEW THUNDERSTORM ACTIVITY IS
FORMING SOUTH OF THE WAVE ITSELF.  PRECIPITABLE WATER VALUES OF
1.1-1.4" EXIST ACROSS THIS AREA PER THE LATEST GPS VALUES.  THE
MORNING SOUNDING OUT OF SOUTHWEST VA SHOWS A SATURATED ATMOSPHERE,
WHICH SHOULD BE ABLE TO TAKE ADVANTAGE OF THE MINIMAL INSTABILITY
AVAILABLE.  BULK SHEAR IN THE 0-6 KM LAYER IS 25-35 KTS PER RECENT
SPC MESOANALYSES.

OVER THE NEXT FEW HOURS, CIN IS EXPECTED TO ERODE AND ATTEMPT TO
LEAD TO MORE SURFACE-BASED CONVECTION CLOSE TO THE FRONTAL WAVE
AND ITS INVERTED TROUGH/STATIONARY FRONT.  SURFACE UPSLOPE FLOW
FROM BOTH SIDES OF THE APPALACHIANS SHOULD AID MOISTURE ADVECTION.
 BREAKS IN THE CLOUD COVER COULD ALLOW CAPE VALUES TO RISE ANOTHER
500 J/KG, WHICH WOULD BRING MLCAPES TO ~1000 J/KG.  CONVECTION IS
EXPECTED TO FORM ON THE NORTHWEST SIDE OF THE INSTABILITY GRADIENT
SHORTLY WHICH WOULD MOVE EAST ACROSS THE TOP OF THE GRADIENT INTO
SOUTHWEST VA.  THE TIMING OF THE CHANGE FROM ELEVATED TO SURFACE
BASED CONVECTION IN VA MAKES THE UNCERTAINTY GREATEST ALONG THE
SOUTHERN PORTIONS OF THE VA BLUE RIDGE CHAIN. HOURLY RAIN RATES UP
TO 1" ARE EXPECTED, AND THE MESOSCALE GUIDANCE SHOWS A DECENT
SIGNAL FOR 2" MAXIMUM AMOUNTS.  SOILS ARE SATURATED FROM RECENT
RAINS.  THE 06Z SSEO NEIGHBORHOOD PROBABILITIES SUGGEST THE
GREATEST THREAT OF HEAVY RAINS IS EXPECTED BETWEEN 17-22Z IN THIS
AREA, WITH 70%+ CHANCE OF THE THREE HOURLY FLASH FLOOD GUIDANCE
VALUES BEING EXCEEDED.

ROTH

ATTN...WFO...JKL...LMK...MRX...RLX...RNK...

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

LAT...LON   38518178 38308057 37847969 36928092 36198227
            35918335 36288382 37128357 37968410 38388263