MESOSCALE DISCUSSION 0670
   NWS STORM PREDICTION CENTER NORMAN OK
   0458 PM CDT SAT APR 30 2011
   
   AREAS AFFECTED...N-CNTRL/NERN TX...FAR SERN OK
   
   CONCERNING...SEVERE POTENTIAL...WATCH LIKELY 
   
   VALID 302158Z - 302330Z
   
   AT LEAST ISOLATED TSTM DEVELOPMENT SHOULD COMMENCE BY 23-00Z ALONG
   COLD FRONT STRETCHING ACROSS N-CNTRL TX. THE COMBINATION OF STRONG
   INSTABILITY AND SHEAR WILL SUPPORT SUPERCELLS WITH PRIMARY INITIAL
   THREATS OF LARGE HAIL AND LOCALLY DAMAGING WINDS. THE PROBABILITY OF
   A WW ISSUANCE BY 00Z IS 60 PERCENT.
   
   21Z SURFACE ANALYSIS PLACED A SLOW-MOVING COLD FRONT FROM NEAR FSM
   TO DFW TO 50 S BWD. RECENT VISIBLE SATELLITE IMAGERY INDICATES CU
   FIELD BECOMING INCREASINGLY AGITATED ALONG THE FRONT ACROSS
   N-CNTRL/CNTRL TX AS SURFACE TEMPERATURES HAVE NOW REACHED THE UPPER
   90S ACROSS THE EDWARDS PLATEAU. DESPITE RELATIVELY NEUTRAL
   UPPER-LEVEL FORCING...MODEST CONVERGENCE ALONG THE FRONT IN
   CONJUNCTION WITH A WEAKLY CAPPED ENVIRONMENT SHOULD BE SUFFICIENT
   FOR ISOLATED TSTM DEVELOPMENT NEAR 23Z...WHICH IS SUPPORTED BY 19Z
   HRRR GUIDANCE.
   
   GIVEN THE PRESENCE OF MLCAPE FROM 2500 TO 3500 J/KG COUPLED WITH
   EFFECTIVE SHEAR OF 40 TO 50 KT...SUPERCELL STRUCTURES SHOULD EVOLVE
   WITH PRIMARY INITIAL THREAT OF LARGE HAIL. WITH STRONGER LOW-LEVEL
   FLOW REMAINING CONFINED TO FAR ERN TX INTO THE LOWER MS
   VALLEY...POTENTIAL FOR TORNADOES SHOULD REMAIN LOW INITIALLY.
   HOWEVER...A W/SWLY STORM MOTION WOULD EVENTUALLY RESULT IN CELL
   PROPAGATION INTO THE STRONGER LOW-LEVEL FLOW/RICHER MOISTURE WITH AN
   ATTENDANT INCREASE IN TORNADIC POTENTIAL.
   
   ..GRAMS.. 04/30/2011
   
   
   ATTN...WFO...LZK...SHV...TSA...FWD...OUN...EWX...
   
   LAT...LON   31149841 32449743 33839649 34709551 34739444 34099401
               33659414 33189452 32589532 31999640 31159744 30959786
               31149841