MESOSCALE PRECIPITATION DISCUSSION 0574
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
235 AM EDT THU AUG 18 2016
 
AREAS AFFECTED...WEST CENTRAL TN 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 180634Z - 181234Z
 
SUMMARY...INCREASING CONVECTIVE COVERAGE IN A HIGHLY EFFICIENT
ATMOSPHERE SHOULD LEAD TO AN INCREASING HEAVY RAINFALL THREAT AND
THE POTENTIAL OF AT LEAST ISOLATED FLASH FLOODING INTO THE EARLY
MORNING HOURS ACROSS CENTRAL TENNESSEE.

DISCUSSION...CURRENT RAP ANALYSIS SHOWS A SUBTLE SHORTWAVE
CURRENTLY LOCATED OVER NORTHEAST ARKANSAS...WITH AN ASSOCIATED
LOCALIZED REGION OF ENHANCED LOW LEVEL WINDS AND MOISTURE
TRANSPORT. THERE IS A GROWING CONSENSUS AMONGST RECENT HRRR AND
PARALLEL HRRR RUNS FOR AN EXPANSION OF CONVECTION ACROSS CENTRAL
TENNESSEE ASSOCIATED WITH THIS FEATURE. PRECIPITABLE WATER IN THIS
AREA IS GENERALLY ABOVE 2"...WITH THE RAP SUGGESTING MOST UNSTABLE
LIFTED INDICES OF AROUND -5C. THUS WOULD APPEAR TO BE PLENTY OF
MOISTURE AND ELEVATED INSTABILITY PRESENT TO SUPPORT CONVECTION
WITH HEAVY RAINFALL RATES.

INDIVIDUAL STORM MOTIONS SHOULD BE PRETTY PROGRESSIVE OFF TO THE
NORTHEAST...HOWEVER GIVEN INCREASED CONVECTIVE COVERAGE...STORM
MERGERS WILL BE POSSIBLE..ALONG WITH MULTIPLE ROUNDS OF CONVECTION
MOVING OVER THE SAME LOCATIONS. RAINFALL TOTALS SHOULD GENERALLY
PEAK AT ABOUT 1-2" IN AN HOUR...ALTHOUGH LOCALIZED AMOUNTS OF UP
TO 2.5" IN AN HOUR ARE POSSIBLE. THE 04Z RUNS OF THE HRRR AND HRRR
PARALLEL MAY BE TOO HIGH WITH THEIR QPF MAGNITUDE...BUT WOULD NOT
BE SURPRISED TO SEE LOCALIZED TOTALS OF 2-4" OVER THE NEXT SEVERAL
HOURS. GIVEN THE INCREASED CONVECTIVE COVERAGE AND EFFICIENT
RAINFALL ENVIRONMENT...WOULD EXPECT AT LEAST AN ISOLATED FLASH
FLOOD THREAT TO EXIST THROUGH THE EARLY MORNING HOURS. GENERALLY
LIKE A BLEND OF THE 05Z HRRR AND HRRRP...WITH BOTH RUNS TRENDING
SLIGHTLY LOWER WITH AMOUNTS AND CONVERGING ON A SIMILAR AXIS THAT
MATCHES RECENT RADAR TRENDS WELL. 

CHENARD

ATTN...WFO...MEG...OHX...

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

LAT...LON   36318613 36158597 35498621 35408643 35248708 
            35168824 35238856 35398912 35678899 35978866 
            36188751 36308646