MESOSCALE PRECIPITATION DISCUSSION 0140...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
205 AM EDT MON APR 24 2017

CORRECTED FOR TYPO ON GRAPHIC

AREAS AFFECTED...CAROLINAS, SOUTHWEST VIRGINIAS, & EASTERN TN

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 240556Z - 241156Z

SUMMARY...A SLOWLY DEEPENING CYCLONE SHOULD LEAD TO HOURLY RAIN
RATES TO 2", WITH LOCAL AMOUNTS OF 3-5", ACROSS PORTIONS OF SC. 
TO THE NORTH, WHERE SOILS ARE SATURATED, CONTINUED MODERATE TO
HEAVY RAIN COULD EXACERBATE FLASH FLOOD/FLOOD ISSUES.

DISCUSSION...A SLOWLY DEEPENING FRONTAL WAVE IS BEING SUPPORTED BY
AN UPPER TROUGH WHICH HAS ACQUIRED A ZERO TILT AS OF LATE ON WATER
VAPOR IMAGERY.  DIRECTIONAL DIVERGENCE CONTINUES TO INCREASE AHEAD
OF THE UPPER TROUGH.  THE MAIN CONVECTIVE LINE IS ELEVATED OVER A
STATIONARY FRONT ACROSS SC AND HAS SHOWN SOME SLOWING AS OF LATE,
AND CELLS ARE BEGINNING TO MERGE IN FROM THE SOUTHEAST WITH NEW
DEVELOPMENT BEGINNING TO TAKE PLACE NEAR THE GA/SC BORDER CLOSE TO
THE SURFACE WAVE.  THE LINE IS ALSO ACQUIRING A LEWP/QLCS
STRUCTURE. IN THE NORTHERN PART OF THE AREA, SATURATED SOILS ARE
INCAPABLE OF ABSORBING RAINS OF MODERATE TO HEAVY INTENSITY --
MUDSLIDES HAVE BEEN REPORTED IN SOUTHWEST VA.   FAIRLY BROAD 25-35
KTS OF 850 HPA INFLOW, CLOSE TO THE MAGNITUDE OF THE 850-400 HPA
MEAN WIND.  MUCAPES OF 500-2000 J/KG LIE NEAR THE GA AND SC
COASTS.  BULK SHEAR OF AROUND 30 KTS HAS LED TO OCCASIONAL SPIN TO
THUNDERSTORMS ALONG THE CONVECTIVE LINE, AND HELP MAINTAIN THE
LINE'S ORGANIZATION.  PRECIPITABLE WATER VALUES OF ~1.5" LIE
ACROSS THE REGION PER GPS VALUES.

THE BACK EDGE OF THE RAIN SHIELD HAS SHOWN SOME RETROGRESSION
ACROSS THE WESTERNMOST CAROLINAS, WESTERN VA, AND EASTERN TN,
WHICH SHOULD CONTINUE AS THE UPPER TROUGH BECOMES NEGATIVELY
TILTED, ITS CYCLONIC CENTER SLIPS SOUTHEAST, AND ORTHOGONAL
UPSLOPE FLOW INCREASES WITH TIME.  WHILE THE CONVECTIVE LINE COULD
CONTINUE MOVING EAST AT ~12 KTS, MORE ACTIVITY IS EXPECTED TO BACK
FILL TO THE WEST ACROSS CENTRAL AND PERHAPS WESTERN SC WHICH HAS
BEEN OCCURRING ACROSS SOUTHERN SC AS OF LATE.  OF CONCERN IS AN
INCREASING MOISTURE/TROPICAL CONNECTION TO A SHEARED CONVECTIVE
LOW NORTH OF GRAND BAHAMA ISLAND, WHICH SHOULD CAUSE PRECIPITABLE
WATER VALUES TO INCREASE TO ~1.75" BY 12Z.  THE OVERALL PATTERN IS
SIMILAR TO THAT OF EARLY OCTOBER 2015, THOUGH THE OVERALL SYSTEM
IS SHOWING GREATER MOVEMENT AND THE EXTRATROPICAL LOW IS STRONGER
THAN THE CONVECTIVE LOW THIS TIME AROUND WHICH SHOULD CAUSE
OVERALL TOTALS TO BE LESS EXTREME ACROSS THE CAROLINAS.  THE
AVAILABLE MOISTURE AND INSTABILITY SUPPORT HOURLY RAIN RATES TO
2", WITH LOCAL AMOUNTS OF 3-5" ADVERTISED BY THE MOST RECENT
MESOSCALE GUIDANCE IN SC THROUGH 12Z (GENERALLY SUPPORTED BY RULES
OF THUMB).  UP NORTH, HOURLY RAIN RATES UP TO 0.4", WITH LOCAL
AMOUNTS OF 1"+ WITHIN THE STRATIFORM RAIN SHIELD WOULD BE MORE
THAN A MATCH FOR THE SATURATED SOILS.  OVERALL, THE THREAT FOR
FLASH FLOODING IS INCREASING.

ROTH

ATTN...WFO...CAE...CHS...FFC...GSP...ILM...JKL...MRX...RAH...
RLX...RNK...

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

LAT...LON   37778053 35467968 34307836 33827794 33677860
            33347898 32887951 32628027 32928162 33478219
            34398303 35198354 36638353 37768213