MESOSCALE DISCUSSION 0538
   NWS STORM PREDICTION CENTER NORMAN OK
   0502 PM CDT SAT APR 23 2011
   
   AREAS AFFECTED...NRN AR...SERN OK
   
   CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY 
   
   VALID 232202Z - 232300Z
   
   INCREASING THUNDERSTORM COVERAGE IS ANTICIPATED OVER THE NEXT FEW
   HRS ACROSS PORTIONS OF SERN OK AND NRN AR...ALTHOUGH STILL SOMEWHAT
   UNCERTAIN DUE TO THE PRESENCE OF AMPLE CLOUD COVER. SHOULD
   CONVECTION BECOME ROOTED IN THE BOUNDARY LAYER...A THREAT OF DMGG
   WINDS...LARGE HAIL...AND PERHAPS ISOLATED TORNADOES WILL LIKELY
   DEVELOP. A TORNADO WATCH WILL LIKELY BE CONSIDERED SOON...AND PARTS
   OF SERN OK CURRENTLY INCLUDED WITHIN SVR WW 187 MAY NEED TO BE
   UPGRADED TO A TORNADO WATCH.
   
   RECENT SATELLITE TRENDS INDICATE SOME ENHANCEMENT IN CONVECTION
   ACROSS ERN OK INTO NWRN AR ACROSS A STALLED FRONT...AIDED BY WEAK
   CONVERGENCE ALONG THE FRONT WITH LOW-LEVEL ISENTROPIC ASCENT FOCUSED
   N OF THE FRONT. ADDITIONALLY...WEAK DEEP-LAYER ASCENT APPEARS TO BE
   OVERSPREADING THE REGION FROM THE SRN PLAINS /PER WATER VAPOR
   IMAGERY/. DESPITE PERSISTENT CLOUD COVER ACROSS THE WARM
   SECTOR...TEMPERATURES HAVE HEATED INTO THE MID-UPPER 70S. AMPLE
   LOW-LEVEL MOISTURE COMBINED WITH THE PRESENCE OF AN EML OVERHEAD HAS
   YIELDED MLCAPE VALUES RANGING BETWEEN 1500-2500 J/KG...WITH LITTLE
   TO NO CINH. SHORT TERM HI-RES MODEL GUIDANCE INDICATES AN UPSWING IN
   SFC-BASED CONVECTION THROUGH 00Z. KINEMATIC FIELDS WILL BE FAVORABLE
   FOR SUPERCELLS...GIVEN EFFECTIVE BULK SHEAR 40-50 KTS.
   ADDITIONALLY...THE POTENTIAL FOR TORNADOES MAY ALSO
   EXIST...PARTICULARLY ALONG THE STALLED FRONT WHERE 0-1 KM SRH
   HELICITY IS MAXIMIZED /200-250 M^2 S^-2/.
   
   ..ROGERS.. 04/23/2011
   
   
   ATTN...WFO...MEG...LZK...SHV...TSA...FWD...OUN...
   
   LAT...LON   35959002 35559153 35209292 34269410 34009450 33859535
               34129605 34419631 35089567 35749493 36119432 36189354
               36309309 36309251 36359157 36449033 35959002