MESOSCALE PRECIPITATION DISCUSSION 0020
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1025 PM EDT SAT APR 27 2013
 
AREAS AFFECTED...NORTHERN TENNESSEE INTO SOUTHERN KENTUCKY 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 280224Z - 280624Z
 
SUMMARY...THE THREAT FOR FLASH FLOODING WILL INCREASE INTO THE
EARLY OVERNIGHT HOURS AS ONGOING HEAVY RAIN OVER WESTERN
TENNESSEE/KENTUCKY APPEARS LIKELY TO SLOWLY SHIFT EAST INTO A
REGION OF SATURATED SOILS.

DISCUSSION...RECENT RADAR IMAGERY CONTINUES TO SHOW CLUSTERS OF
MODERATE TO HEAVY RAIN JUST EAST OF THE MISSOURI BOOT
HEEL...MAINLY ALONG AND NORTH OF A SLOW MOVING WARM FRONT...WHICH
EXTENDED FROM WESTERN TENNESSEE INTO SOUTHERN GEORGIA AT 02Z.
MOISTURE IN THE WARM SECTOR IS CHARACTERIZED BY PWATS IN THE 1.25
TO 1.50 INCH RANGE AS PER 00Z RAOB FROM BMX...WHICH CONTINUES TO
OVERRUN THE WARM FRONT VIA BROAD FLOW IN THE LOW LEVELS ON THE
ORDER OF 20 TO 30 KTS FROM THE SOUTHWEST. 

BOTH GLOBAL AND HI-RES MODEL QPF HAS BEEN POOR IN HANDLING THIS
SITUATION WHICH LOWERS CONFIDENCE...HOWEVER RECENT TRENDS IN
OBSERVATIONS INDICATE ONGOING HEAVY RAIN OVER TENNESSEE/KENTUCKY
WILL GRADUALLY SHIFT TOWARD THE EAST OVER THE NEXT FEW HOURS. THE
BROAD LOW LEVEL OVERRUNNING FLOW MENTIONED ABOVE IS EXPECTED TO
PERSIST OVERNIGHT AHEAD OF A SLOW MOVING COLD FRONT PER SHORT TERM
GUIDANCE. IN ADDITION...CONVECTION APPEARS TO BE DEVELOPING
BENEATH A REGION OF DIFLUENT FLOW IN THE 200-300 MB LAYER...WHICH
WILL SLOWLY MOVE EAST OVER THE HIGHLIGHTED FLASH FLOOD THREAT
AREA. THROUGH 06Z. CURRENT FLASH FLOOD GUIDANCE VALUES ARE
GENERALLY 1 IN/HR AND 1.5 IN/3HR WHICH HAS ALREADY BEEN MET OVER
WESTERN TENNESSEE PER CO-OP REPORTS AND WITH REPORTS OF ONGOING
FLASH FLOODING NEAR THE TENNESSEE/KENTUCKY BORDER.

OTTO


ATTN...WFO...LMK...OHX...PAH...MEG...

LAT...LON   35718626 35618707 35738767 35758844 35778878 35918894
            36098879 36338819 36518763 36758696 37098622 37078563
            36658520 36238528 35908579 35718626