MESOSCALE DISCUSSION 2139
   NWS STORM PREDICTION CENTER NORMAN OK
   1238 PM CST SUN DEC 09 2012
   
   AREAS AFFECTED...SWRN INTO NERN AR...SERN MO...FAR SRN IL...WRN
   KY/TN
   
   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 
   
   VALID 091838Z - 092045Z
   
   PROBABILITY OF WATCH ISSUANCE...40 PERCENT
   
   SUMMARY...PORTIONS OF SWRN INTO NERN AR...SERN MO...FAR SRN IL...AND
   WRN KY/TN ARE BEING MONITORED FOR A WW THIS AFTERNOON. PRIMARY SVR
   WEATHER THREAT WILL BE LARGE HAIL/DAMAGING WIND GUSTS...THOUGH A
   TORNADO OR TWO WILL ALSO BE POSSIBLE.
   
   DISCUSSION...EARLY AFTERNOON SURFACE ANALYSIS PLACES AN AREA OF LOW
   PRESSURE OVER CNTRL AR...WITH A COLD FRONT EXTENDING SWWD INTO CNTRL
   TX...AND A WARM FRONT SLOWLY RETREATING NWD OVER WRN/CNTRL KY. AS AN
   UPPER TROUGH CONSOLIDATES AND DEEPENS OVER THE CNTRL CONUS THIS
   AFTERNOON/EVENING...THE SURFACE LOW IS FORECAST TO EJECT NEWD INTO
   THE LOWER OH VALLEY...AND THE WARM FRONT WILL CONTINUE LIFTING NWD
   INTO SRN IND/OH. 
   
   MEANWHILE...A 30-40 KT SWLY LLJ HAS AIDED IN TRANSPORTING LOW TO MID
   60F DEWPOINTS ALONG AN AXIS FROM SWRN AR INTO WRN KY/TN. IN
   ADDITION...POCKETS OF CLEARING OVER AR HAVE ALLOWED TEMPERATURES TO
   LOCALLY WARM TO AROUND 70F...WHICH HAS AIDED IN BOUNDARY LAYER
   DESTABILIZATION AND THE DEVELOPMENT OF AGITATED CUMULUS CLOUD
   STREETS. WV AND VIS SATELLITE IMAGERY SHOW A PLUME OF HIGH LEVEL
   CLOUDINESS OVERSPREADING THE REGION...WHICH MAY INFER THE APPROACH
   OF A SUBTLE UPPER-LEVEL DISTURBANCE. ASCENT ASSOCIATED WITH THAT
   FEATURE COMBINED WITH CONTINUED SURFACE HEATING...CONTRIBUTING
   TOWARD SBCAPE VALUES FROM 500-1500 J/KG...MAY AID IN GRADUAL
   DEEPENING OF THE CUMULUS FIELD OVER AR AND EVENTUAL SCATTERED
   THUNDERSTORM DEVELOPMENT BY MID AFTERNOON.
   
   OTHERWISE...ASCENT ALONG THE COLD FRONT WILL STRENGTHEN BY LATE
   AFTERNOON/EVENING...AND BE SUFFICIENT FOR THE DEVELOPMENT OF
   SCATTERED TO NUMEROUS STORMS FROM WRN KY INTO SRN AR. IF CELLULAR
   ACTIVITY CAN DEVELOP DURING THE AFTERNOON...THEN DEEP-LAYER SHEAR
   NEAR 50 KT WILL FAVOR SUPERCELLS. IF STORMS QUICKLY ORGANIZE INTO
   LINES ALONG THE FRONT LATE THIS AFTERNOON/EVENING...THEN BOWING/LEWP
   STRUCTURES WILL BE MORE LIKELY. LARGE HAIL AND DAMAGING WIND GUSTS
   WILL BE THE PRIMARY SVR WEATHER THREATS WITH EITHER MODE OF
   CONVECTION. HOWEVER...A TORNADO OR TWO WILL BE POSSIBLE AS THE 30-40
   KT SWLY LLJ AIDS IN EFFECTIVE SRH VALUES FROM 150-250 M2 S-2.
   
   ..GARNER/HART.. 12/09/2012
   
   
   ATTN...WFO...PAH...MEG...LZK...SGF...SHV...
   
   LAT...LON   34079436 35209349 36749090 37378894 37028801 35708856
               33819192 33339390 34079436