MESOSCALE PRECIPITATION DISCUSSION 0366
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
938 AM EDT WED JUN 27 2018

AREAS AFFECTED...CENTRAL AND EASTERN TN

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

VALID 271340Z - 271700Z

SUMMARY...CONVECTION TRAINING IN A HIGH MOISTURE CONTENT
ENVIRONMENT COULD PRODUCE HOURLY RAINFALL RATES NEAR 2.00 INCHES,
WHICH IN TURN MAY POSE A FLASH FLOOD THREAT THIS MORNING.

DISCUSSION...CONVECTION IS SLOWLY INCREASING IN COVERAGE ACROSS
PORTIONS OF CENTRAL INTO EASTERN TN THIS MORNING... AHEAD OF A
SHORT WAVE LOCATED OVER WEST CENTRAL TN (BASED ON THE GOES-16 WV
LOOP). THE CONVECTION IS FORMING/MOVING ALONG AN AXIS OF 2.00 INCH
PRECIPITABLE WATER AIR (28/12Z BNA SOUNDING SHOWED A PRECIPITABLE
WATER VALUE OF 2.10 INCHES...ALONG WITH A MOIST COLUMN THROUGH 500
MB). IN THIS DEEP MOISTURE...THE KOHX RADAR CONTINUES TO INDICATE
HOURLY RAINFALL RATES BETWEEN 1.50 AND 2.00 INCHES.
HOWEVER...BASED ON THE RADAR PRESENTATION (AS WELL AS THE OHX HCA
PRODUCT)...THESE AMOUNTS COULD BE HAIL CONTAMINATED).

THUS FAR...INSTABILITY HAS BEEN THE LIMITING FACTOR FOR THE SLOW
INCREASING CONVECTIVE COVERAGE. HOWEVER...RAP SOUNDINGS ACROSS
EASTERN TN SHOWED INSTABILITY INCREASING SLOWLY THROUGH
27/17Z...WHICH COULD ALLOW THE COVERAGE TO EXPAND. THE CONVECTION
IS MOVING ALONG FROM WEST TO EAST...ALONG WITH THE 850-300 MB
FLOW. THE MOST RECENT RAP SUGGESTS THAT WHILE THIS MOTION
CONTINUES...PROPAGATION VECTORS COULD ALLOW FOR CONVECTION TO
TRAIN OVER CENTRAL INTO EASTERN TN...WHICH RAISES THE THREAT FOR
FLASH FLOODING.

THE HRRR/EXPERIMENTAL HRRR HAVE HAD THE BEST HANDLE ON THE
CONVECTION (WHILE THE 00Z WRF-ARW/00Z WRF-NMMB SHOWED VERY LITTLE
WHERE THE CONVECTION IS OCCURRING NOW). THE HRRR INDICATED THE
POTENTIAL FOR LOCAL 2.00/3.00 INCHES OF RAINFALL OVER EASTERN TN
BEFORE THE CONVECTION MOVES EAST. TRAINING COULD BE REQUIRED FOR
RAINFALL AMOUNTS THIS HIGH...SO AT THIS POINT FLASH FLOODING IS
ONLY CONSIDERED POSSIBLE.

HAYES

ATTN...WFO...GSP...JKL...LMK...MRX...OHX...

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

LAT...LON   36658258 36498199 36048188 35408290 35448567
            36098578 36648516