MESOSCALE PRECIPITATION DISCUSSION 0288
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
442 AM EDT MON AUG 18 2014
 
AREAS AFFECTED...PORTIONS OF EASTERN TN AND WESTERN NC 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 180841Z - 181311Z
 
SUMMARY...THUNDERSTORMS HAVE BEGUN TO DEVELOP ACROSS SOUTH-CENTRAL
TN.  CONSIDERING A GROWING SIGNAL IN THE MESOSCALE QPF GUIDANCE
FOR HEAVY RAINFALL IN EASTERN TN AND WESTERN NC, FLASH FLOODING IS
POSSIBLE IN THIS REGION.

DISCUSSION...SCATTERED THUNDERSTORMS WITH COOLING CLOUD TOPS HAVE
BEGUN TO DEVELOP ACROSS SOUTH-CENTRAL TN WITHIN A MOISTURE PLUME
WITH PRECIPITABLE WATER VALUES OF ~2" -- ABOVE THE 90TH PERCENTILE
FOR MID AUGUST.  ALSO, 850 HPA INFLOW OF 30 KNOTS LIES WITHIN THIS
REGION, WHICH IS 50% GREATER THAN THE 850-400 HPA MEAN WINDS IN
THIS REGION PER THE 06Z NAM GUIDANCE.  THIS ACTIVITY SEEMS TO BE
ELEVATED OVER AN OUTFLOW BOUNDARY -- SEEN MOSTLY IN THE SURFACE
TEMPERATURE PATTERN -- LEFT OVER FROM EVENING THUNDERSTORM
ACTIVITY ACROSS WESTERN TN, NORTHERN MS, AND NORTHERN AL. AN AREA
OF 500-1000 J/KG MUCAPE WAS SEEN ACROSS CENTRAL TN IN THE LATEST
SPC MESOANALYSIS PAGE.  THESE VARIABLES BARELY MEET THE CRITERIA
FOR THE WET MULTICELL ENVIRONMENT.  WIND FLOW IS UNIDIRECTIONAL
WITH HEIGHT, WHICH IS A SIGNATURE FOR HEAVY RAINFALL/CELL
TRAINING.  THERE HAS ALSO BEEN SOME INDICATION OF BACKBUILDING OF
CELLS IN RECENT RADAR ANIMATIONS.

THE EXPECTATION IS THAT THIS ACTIVITY WILL MOVE EASTWARD ACROSS
EASTERN TN INTO WESTERN NC -- INTERACTING WITH A WEAK WARM
FRONT/LEADING EDGE OF A WEAK SURFACE WEDGE -- BEFORE FADING IN THE
12-13Z TIME FRAME DUE TO FADING INSTABILITY.  AVAILABLE MOISTURE
VALUES INDICATE HOURLY RAINFALL RATES UP TO 2.5" ARE POSSIBLE IN
THIS REGION.  WITH GROWING SUPPORT AMONGST THE MOST RECENT
MESOSCALE QPF GUIDANCE OF 2-4" OF RAINFALL LOCALLY, WHICH WOULD
EXCEED THE FLASH FLOOD GUIDANCE IN THIS REGION, BELIEVE FLASH
FLOODING IS POSSIBLE DUE TO CELL TRAINING.

ROTH

ATTN...WFO...GSP...MRX...FFC...OHX...HUN...

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

LAT...LON   34568640 34688741 34858780 35528782 36038721 36138541
            35998286 35728214 35138243 34568385 34568640