MESOSCALE DISCUSSION 0826
   NWS STORM PREDICTION CENTER NORMAN OK
   1208 PM CDT FRI MAY 20 2011
   
   AREAS AFFECTED...NRN AND CENTRAL TX
   
   CONCERNING...SEVERE POTENTIAL...WATCH LIKELY 
   
   VALID 201708Z - 201815Z
   
   WW WILL LIKELY BE REQUIRED WITHIN THE NEXT 1-2 HOURS /BY 18-19Z/. 
   PROBABILITY OF WATCH ISSUANCE IS 80 PERCENT.
   
   AT 17Z...REGIONAL RADAR IMAGERY AND LIGHTNING DATA SHOWED A STRONG
   STORM ALONG THE SRN EXTENT OF A CONVECTIVE OUTFLOW BOUNDARY
   ATTENDANT TO THE SRN PLAINS MCS...WITH THIS STORM LOCATED IN NRN SAN
   SABA/WRN MILLS COUNTIES.  VISIBLE SATELLITE IMAGERY SHOWED BREAKS IN
   THE CLOUDS ALONG AND EAST OF THE ABOVE MENTIONED BOUNDARY...
   SUPPORTING SURFACE HEATING WITHIN RICH BOUNDARY LAYER MOISTURE
   /SURFACE DEWPOINTS IN THE LOWER 70S/.  STEEP MIDLEVEL LAPSE RATES
   /7.5-8.5 C PER KM/ AND ADDITIONAL HEATING WILL MAINTAIN STRONG
   INSTABILITY /MLCAPE 2000-3000 J PER KG/ THROUGH THE AFTERNOON. 
   ALTHOUGH LOW LEVEL WINDS TEND TO WEAKEN WITH SWD EXTENT ACROSS
   TX...THE ERN EXTENT OF STRONGER MID AND HIGH LEVEL SLY FLOW WILL
   RESULT IN EFFECTIVE BULK SHEAR SUPPORTIVE OF ORGANIZED STORMS...
   INCLUDING SUPERCELLS.  LARGE HAIL AND DAMAGING WINDS WILL BE THE
   PRIMARY THREATS WITH ADDITIONAL STORMS EXPECTED TO DEVELOP ALONG THE
   COMPOSITE OUTFLOW BOUNDARY EXTENDING FROM SOUTH CENTRAL TO NORTH
   CENTRAL TX.
   
   ..PETERS.. 05/20/2011
   
   
   ATTN...WFO...SHV...HGX...FWD...OUN...EWX...SJT...
   
   LAT...LON   30299951 31359957 33259790 33779690 33729545 31939563
               30839596 29969678 29459782 29619918 30299951