MESOSCALE PRECIPITATION DISCUSSION 0549
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1005 PM EDT SAT OCT 03 2015
 
AREAS AFFECTED...PORTIONS OF SC, WESTERN NC, & NORTHEAST GA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 040204Z - 040804Z
 
SUMMARY...RAINFALL COVERAGE, EXPANSION, AND INTENSIFICATION HAS
BEEN SEEN ACROSS SC OVER THE PAST COUPLE HOURS.  CATASTROPHIC
FLASH FLOODING COULD OCCUR.

DISCUSSION...PER SATELLITE IMAGERY, RIPPLES OF SHORTWAVE ENERGY
ARE MOVING UP A WARM CONVEYOR BELT/ATMOSPHERIC RIVER WHICH
CONNECTS AN OCCLUDED CYCLONE NEAR CHARLESTON TO HURRICANE JOAQUIN.
 WITHIN THE ATMOSPHERIC RIVER, LOW-LEVEL DIRECTIONAL CONVERGENCE
IS SIGNIFICANT.  INFLOW AT 850 HPA IS 30-50 KTS (ROUGHLY 15 KTS
LOWER THAN INDICATED ON THE 02/12Z MODEL GUIDANCE), NEAR THE
MAGNITUDE OF THE MEAN 850-400 HPA WIND.  PRECIPITABLE WATER VALUES
IN THE REGION ARE 1.7-2.3" PER GPS VALUES, AROUND 1.5 SIGMAS ABOVE
THE MEAN FOR EARLY OCTOBER.  MUCAPE VALUES OF 1000-2000 J/KG NEAR
THE SC COAST, WHICH ARE ADVECTING FARTHER INLAND AS CIN DEVELOPS
ACROSS THE REGION.  A COASTAL FRONT JUST INSIDE THE SC/NC COAST
HAS STALLED AS OF LATE AND IS ACTING AS THE FOCUS FOR CONVECTION
WITH THE HIGHEST RAINFALL RATES.  AN OBSERVATION NEAR CHARLESTON
SC INDICATES RECENT RAIN RATE OF 3" AN HOUR, WITH A STORM TOTAL
NEAR 15" -- LIKELY THE WETTEST STORM ON RECORD FOR THE CHARLESTON
AREA.

THE CAM GUIDANCE INDICATES THAT LOCAL AMOUNTS OF 3-7" ARE POSSIBLE
WITHIN THIS REGION OVER THE NEXT SEVERAL HOURS, WHICH COULD FALL
QUICKLY.  DESPITE THEIR HIGH BIAS BETWEEN 20Z AND 02Z, THE CAM
GUIDANCE LOOKS MORE REALISTIC IN THEIR PORTRAYAL OF PRECIPITATION
OVER THE NEXT SIX HOURS.  RAIN RATES OF 3" AN HOUR COULD MIGRATE
FARTHER INTO THE INTERIOR OF SC, WITH 1.5" AN HOUR RAIN RATES
POSSIBLE IN THE SOUTHERNMOST APPALACHIANS WHERE INSTABILITY IS
FARTHER AFIELD.  RAIN RATES THIS HIGH WOULD CREATE SIGNIFICANT
PROBLEMS IN URBAN AREAS SUCH AS CHARLESTON,
GREENVILLE/SPARTANBURG, COLUMBIA, AUGUSTA, AND THE ATLANTA
SUBURBS.  RADAR ESTIMATES REMAIN QUITE LOW IN THIS REGION, RUNNING
ROUGHLY 30-50% BELOW ACTUAL REPORTS.  SOILS CONTINUE TO SATURATE
ACROSS NORTHEAST GA AND NORTHWEST SC WHERE RAINFALL HAS BEEN LESS
HEAVY.  CONSIDERING THE RAINFALL EXPECTED, CATASTROPHIC FLASH
FLOODING ALONG WITH ASSOCIATED LANDSLIDES AND MUDSLIDES IN THE
TERRAIN REMAIN A DISTINCT POSSIBILITY.

ROTH

ATTN...WFO...CAE...CHS...FFC...GSP...ILM...MRX...

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

LAT...LON   35538361 35288238 34978141 34037951 33507903 
            33087920 32547997 32438121 33078314 34148437 
            34898463 35398408