MESOSCALE PRECIPITATION DISCUSSION 0690
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
147 PM EDT MON AUG 14 2017

AREAS AFFECTED...NORTH GA, WESTERN CAROLINAS, & EASTERN TN

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

VALID 141747Z - 142347Z

SUMMARY...THUNDERSTORMS ARE EXPECTED TO EXPAND IN COVERAGE WITH
TIME.  HOURLY RAIN TOTALS TO 2.5" WITH LOCAL AMOUNTS TO 4" ARE
POSSIBLE WHERE CELLS MERGE/TRAIN.

DISCUSSION...A CIRCULATION ALOFT IS MOVING THROUGH CENTRAL TN AND
LIKELY ACTING AS A SOURCE OF DIVERGENCE ALOFT.  SUNNY SKIES ARE
LEADING TO INCREASING INSTABILITY.  AT THE SURFACE, A WEAK THERMAL
WAVE IS MOVING INTO NORTHWEST GA WITH A THERMAL BOUNDARY RETURNING
NORTHWARD.  NEAR AND AHEAD OF THE BOUNDARY, SHOWERS AND
THUNDERSTORMS ARE DEVELOPING.  PRECIPITABLE WATER VALUES OF 1.5-2"
LIE HERE PER GPS VALUES AND RAP INITIALIZATIONS.  ML CAPE VALUES
OF 500-1000 J/KG LIE ACROSS MUCH OF THE AREA, WITH HIGHER VALUES
OF 2000 J/KG IN NORTHEAST GA.  INFLOW AT 850 HPA IS WEST-SOUTHWEST
AT 10 KTS PER VAD WIND PROFILES, BUT EFFECTIVE BULK SHEAR IS ~30
KTS PER SPC MESOANALYSES WHICH IS TWICE THE VALUE OF THE MEAN
850-400 HPA WIND.

THE MESOSCALE GUIDANCE SHOWS SPOTTY LOCAL AMOUNTS OF 2-4", WHICH
APPEARS POSSIBLE GIVEN THE ABOVE FACTORS.  AS THE TN CIRCULATION
APPROACHES, LOW-LEVEL INFLOW IS EXPECTED TO RISE TOWARDS 20 KTS
WHICH IN ADDITION TO THE BULK SHEAR AND RISING PRECIPITABLE WATER
VALUES SHOULD HELP INCREASE CONVECTIVE COVERAGE AND COULD LEAD TO
SHORT TRAINING BANDS WITHIN THE TOPOGRAPHY AS THE FLOW IS NEARLY
UNIDIRECTIONAL WITH HEIGHT.  HOURLY RAIN TOTALS UP TO 2.5" APPEAR
POSSIBLE WHERE CELLS TRAIN AND/OR MERGE.  ABOVE AVERAGE RAINFALL
HAS BEEN SEEN OVER THE PAST COUPLE WEEKS; SOILS ARE PARTIALLY
SATURATED WITHIN THE RUGGED TERRAIN.

ROTH

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

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

LAT...LON   36948265 36438109 34898184 33568237 33558372
            34408502 35318522