MESOSCALE DISCUSSION 0471
   NWS STORM PREDICTION CENTER NORMAN OK
   0140 PM CDT TUE APR 19 2011
   
   AREAS AFFECTED...PORTIONS OF WRN AR / ERN OK / N-CNTRL TX
   
   CONCERNING...SEVERE POTENTIAL...WATCH LIKELY 
   
   VALID 191840Z - 191945Z
   
   A TORNADO WATCH WILL LIKELY BE REQUIRED BY MID AFTERNOON.  STORM
   INITIATION IS FIRST EXPECTED OVER ERN OK/NWRN AR ALONG COLD FRONT. 
   LARGE TO VERY LARGE HAIL AND DMGG WINDS WILL BE THE PRIMARY HAZARDS
   BUT AN ISOLD TORNADO RISK SEEMS TO BE EVOLVING...ESPECIALLY OVER ERN
   OK AND THEN EVENTUALLY INTO WRN AR AND PERHAPS FAR NERN TX.
   
   18Z SURFACE ANALYSIS PLACES A COLD FRONT LOCATED FROM NEAR JLN SWWD
   NEAR ADM WITH AN ATTENDANT DRYLINE EXTENDING SWD NEAR THE AUS AND
   SAT VICINITY.  THE AIRMASS HAS BECOME QUITE UNSTABLE AHEAD OF THE
   EWD MOVING SURFACE FEATURES WITH MLCAPE ALREADY 3000-4000 J/KG /PER
   OBJECTIVE ANALYSIS/ AND EXPECTED TO INCREASE AND BECOME EXTREMELY
   UNSTABLE AS TEMPS CLIMB WELL INTO THE 80S/90S.  WATER VAPOR IMAGERY
   SHOWS A SHORTWAVE TROUGH CURRENTLY MOVING INTO WRN OK AND HEIGHT
   FALLS ASSOCIATED WITH THE DISTURBANCE MAY GLANCE THE REGION AS FAR S
   AS N-CNTRL TX.  THIS COMBINED WITH HEATING AND LOW LEVEL
   CONVERGENCE/FRONTAL LIFT WILL ENABLE THE CAP TO ERODE INITIALLY
   ACROSS ERN OK/FAR NWRN AR WHERE CU ARE ALREADY BECOMING AGITATED
   ALONG THE BOUNDARY AND WHERE STORM COVERAGE WILL LIKELY BE GREATEST
   /N OF THE RED RIVER/.  FARTHER S...THE CAP IS EXPECTED TO BE
   BREACHED LOCALLY--RESULTING IN WIDELY SCATTERED STORMS.  GIVEN THE
   VERY UNSTABLE AIRMASS AND INCREASING MID-UPPER WSWLY/S...UPDRAFTS
   WILL RAPIDLY DEVELOP WITH SUPERCELLS THE FAVORED STORM MODE.  A
   LARGE TO VERY LARGE HAIL THREAT WILL LIKELY EXIST...IN ADDITION TO
   DMGG WINDS AND SOME TORNADO POTENTIAL.  THE TORNADO RISK APPEARS
   GREATEST GENERALLY OVER OK/AR/FAR NERN TX WHERE LOW LEVEL FLOW IS
   FORECAST TO BE STRONGEST.
   
   ..SMITH.. 04/19/2011
   
   
   ATTN...WFO...LZK...SHV...TSA...FWD...OUN...
   
   LAT...LON   32939727 34319675 35319583 36149495 36359444 36369372
               35969327 35309328 34699361 34059420 32369598 32279653
               32439710 32939727