MESOSCALE PRECIPITATION DISCUSSION 0055
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
824 PM EDT MON MAY 20 2013
 
AREAS AFFECTED...NORTH-CENTRAL TX...SOUTHEAST OK...WESTERN AR 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 210023Z - 210400Z
 
SUMMARY...INCREASING POTENTIAL FOR BACK-BUILDING AND REPEATING
CONVECTION OVER THE NEXT SEVERAL HOURS ALONG WITH CELL-MERGERS.
EXPECTING PERSISTENT CONVECTION TO ENHANCE THE FLASH FLOOD
POTENTIAL THROUGH THE EVENING HOURS.

DISCUSSION...A CLUSTER OF SEVERE THUNDERSTORMS INVOF THE RED RIVER
VALLEY OF N CNTRL TX IS SEEN BACK-BUILDING ATTM IN RESPONSE TO A
VERY UNSTABLE AIRMASS OVER MUCH OF CNTRL TX JUST EAST OF A VERY
WELL-DEFINED DRYLINE. AN AXIS OF VERY HIGH CAPE...EXCEEDING 4000
J/KG IS SEEN ACROSS THIS REGION AND SOUTH-SOUTHWEST OF THE AREA OF
ACTIVE DEEP CONVECTION. GOES-SOUNDER AND GPS PWATS ARE AS HIGH AS
1.3 INCHES OVER THIS AREA...AND THAT HAS BEEN SEEN SLOWLY
INCREASING THE LAST COUPLE OF HOURS WITH A PERSISTENT
SOUTH-SOUTHEAST LOW LEVEL FETCH OF MOISTURE. 

THE CONCERN OVER THE NEXT SEVERAL HOURS IS THAT THIS AREA OF
CONVECTION WILL BE IN A PRIME POSITION TO BACKBUILD AND REPEAT
OVER THE SAME AREA AS AN UPSTREAM SHORTWAVE TROUGH DIGGING EAST
INTO THE FAR WEST TX HIGH PLAINS OVERNIGHT FOSTERS A FAVORABLE
DOWNSTREAM AXIS OF UPPER LEVEL DIV/LARGE SCALE ASCENT...WITH
SUFFICENT FORCING TO SUSTAIN THE ONGOING CONVECTIVE THREAT WELL
THROUGH THE EVENING HOURS. ALREADY SEEING THIS EVIDENCED IN LATEST
IR/WV IMAGERY WITH CONVECTIVE-V SIGNATURES. DESPITE THE GRADUAL
INCREASE IN SBCIN WITH THE LOSS OF DIURNAL HEATING...EXPECTING
MLCAPE VALUES TO REMAIN RATHER HIGH THROUGH THE EVENING...AND WITH
A STEADY FEED OF LOW LEVEL MOISTURE...THE THERMODYNAMIC
ENVIRONMENT WILL REMAIN CONDUCIVE FOR SUSTAINABLE CONVECTION. THE
18Z NAM-CONEST IN PARTICULAR IS HIGHLIGHTING THIS SCENARIO AND
ALREADY APPEARS TO BE HANDLING THE ONGOING CONVECTION WELL.
RAINFALL RATES OF OVER 2 INCHES/HR ARE POSSIBLE...AND FLASH
FLOODING WILL BE POSSIBLE WHERE BACK-BUILDING AND REPEATING OF
CELLS OCCUR INCLUDING CELL-MERGERS. WILL CONTINUE TO MONITOR.

ORRISON


ATTN...WFO...LZK...SHV...TSA...FWD...OUN...

LAT...LON   34209733 34689609 35239476 35179387 34629376 34159424
            33829493 33559586 33389706 33369804 33669821 33909809
            34209733