MESOSCALE PRECIPITATION DISCUSSION 0423
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1201 PM EDT TUE OCT 14 2014
 
AREAS AFFECTED...WRN NC...WRN SC...NRN GA...ERN TN...SW VA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 141600Z - 142100Z
 
SUMMARY...LOW-TOPPED CONVECTION WITHIN AN INCREASINGLY TROPICAL
AIRMASS MAY BEGIN TO PRODUCE FLASH FLOODING ON 3 TO 6 HOUR TIME
SCALES.

DISCUSSION...INSTABILITY WILL REMAIN MINIMAL IN THIS AREA. THE
ATMOSPHERE WILL COMPENSATE WITH LARGE SCALE DEEP-LAYER LIFT AHEAD
OF AN UPPER TROUGH AND FORCED LOW-LEVEL ASCENT OWING TO 45-55 KNOT
UPSLOPE FLOW AT 850 MB. AT 1530Z THE NUMBER OF CONVECTIVE UPDRAFTS
WAS INCREASING PER RADAR OBSERVATIONS...ALL THE WAY FROM WESTERN
NC INTO AREAS THAT HAD ALREADY BEEN CONVECTIVELY OVERTURNED IN WRN
GA. THIS AXIS REPRESENTS A BROAD WARM CONVEYOR BELT THAT WILL
CARRY INCREASINGLY TROPICAL AIR INTO THE GA PIEDMONT AND THE
MOUNTAINOUS AREAS TO THE N AND NE. WHILE MOUNTAINS IN GA/SC/NC
WILL INTERCEPT MUCH OF THE MOISTURE...STRONG ADVECTION THROUGH A
DEEP LAYER MAY RESULT IN SOME SPILLOVER OF HEAVIER RAINFALL INTO
TN...WHERE FLASH FLOOD GUIDANCE IS LESS. THE HEAVY RAIN CONCERN
WILL ALSO MIGRATE GRADUALLY TOWARD SW VA AS THE PRECIPITABLE WATER
GRADIENT MOVES NORTHWARD. BY MID AFTERNOON, RAP SOUNDINGS IN THE
OUTLINED AREA INDICATE DEEPLY SATURATED PROFILES BUT WITH
CONVECTIVE LAPSE RATES MAINTAINED BY STRONG LIFT...ALL WHILE PW
VALUES RISE TO 1.6 - 1.9".

MESOSCALE MODELS ARE UNANIMOUS IN PLACNG AT LEAST 2 - 3.5" OF RAIN
ALONG THE SOUTHWARD FACING SLOPES IN THIS REGION THROUGH EARLY
EVENING. RISING PW VALUES AND DEEP SATURATION WILL YIELD HIGH
EFFICIENCY AND PERHAPS HEAVIER AMOUNTS THAN ARE BEING MODELED.
THIS AREA HAS NOT BEEN ESPECIALLY WET IN RECENT WEEKS...BUT FLASH
FLOOD GUIDANCE VALUES COULD BE MET ON 3 TO 6 HOUR TIME SCALES.

BURKE

ATTN...WFO...CAE...FFC...GSP...MRX...RAH...RLX...RNK...

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

LAT...LON   37188077 36888030 36068039 34518173 33918272 
            33928434 34768453 35758390 36698282 37058226 
            37188151