MESOSCALE DISCUSSION 0487
   NWS STORM PREDICTION CENTER NORMAN OK
   0536 PM CDT FRI APR 18 2003
   
   AREAS AFFECTED...SW OK AND NWRN TX
   
   CONCERNING...SEVERE THUNDERSTORM POTENTIAL 
   
   VALID 182236Z - 190030Z
   
   ...TSTMS ARE EXPECTED TO DEVELOP IN THE NEXT FEW HOURS WITH LARGE
   HAIL THE MAIN THREAT...
   
   TCU ARE INCREASING ON NORTH SIDE OF SUBTROPICAL CI PLUME FROM
   KNOX COUNTY TX INTO SWRN OK NEAR FDR AND APPEAR TO BE ALONG NWRN
   PERIPHERY OF INCREASING SURFACE DEW POINTS. LATEST RUC SOUNDINGS
   SUGGEST THAT CINH HAS NEARLY ERODED AND STRONGEST SURFACE
   CONVERGENCE IS DEVELOPING ALONG THIS CLOUD LINE.  THUS...IT IS
   POSSIBLE THAT ISOLD-WDLY SCATTERED TSTMS COULD INITIATE IN THE
   NEXT COUPLE OF HOURS.  THE TSTMS ARE LIKELY TO BE HIGH BASED LOW
   PRECIPITATION SUPERCELLS EARLY THIS EVENING GIVEN MEAGER MOISTURE
   IN PLACE AND DEEP LAYER SHEAR VALUES IN EXCESS OF 45 KTS.  
   
   MORE CONFIDENCE EXISTS FOR A MORE RAPID INCREASE IN TSTMS AFTER
   SUNSET AS WARM/MOIST ADVECTION STRENGTHENS ACROSS NWRN TX INTO
   SWRN/CNTRL OK.	INCREASING INSTABILITY...STRONG DEEP LAYER SHEAR
   AND INCREASING ASCENT DOWNSTREAM OF APPROACHING SHORTWAVE TROUGH
   WILL BRING A THREAT OF LARGE HAIL...DAMAGING WINDS AND PERHAPS AN
   ISOLD TORNADO.	ANOTHER MESOSCALE DISCUSSION WILL LIKELY BE
   ISSUED IN A COUPLE HOURS AFTER EVENING RAOB DATA IS ANALYZED.
   
   
   ..RACY.. 04/18/2003
   
   
   ATTN...WFO...FWD...OUN...SJT...LUB...
   
   33870025 34559979 35029863 35139788 34499761 34029780
   33549848 33169901 32539982 32610019