MESOSCALE DISCUSSION 0509
   NWS STORM PREDICTION CENTER NORMAN OK
   0322 AM CDT SAT APR 18 2009
   
   AREAS AFFECTED...EDWARDS PLATEAU/HILL COUNTRY/RIO GRANDE VALLEY
   REGIONS OF TX
   
   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 
   
   VALID 180822Z - 181015Z
   
   STORMS/SEVERE THREAT SHOULD CONTINUE TO INCREASE ACROSS PARTS OF
   CENTRAL/SWRN TX OVER THE NEXT FEW HOURS...POSSIBLY REQUIRING WW
   ISSUANCE.
   
   ISOLATED STORM DEVELOPMENT IS ONGOING ATTM ON BOTH THE U.S. AND
   MEXICAN SIDE OF THE RIO GRANDE...FROM ROUGHLY DEL RIO TO LAREDO...IN
   REGION OF SLOWLY INCREASING LARGE-SCALE ASCENT IMPLIED BY CURRENT WV
   LOOP.  THIS IS OCCURRING ON THE SERN FRINGE OF THE UPPER LOW OVER
   THE SRN ROCKIES -- LIKELY INVOF A SMALL UPPER FEATURE ROTATING
   AROUND THIS LARGER-SCALE LOW.  WITH EVENING RAOBS REVEALING STEEP
   MID-LEVEL LAPSE RATES...SUBSTANTIAL CAPE INDICATED ABOVE THE MORE
   STABLE BOUNDARY LAYER WILL LIKELY SUPPORT ADDITIONAL/VIGOROUS
   UPDRAFTS -- AIDED BY DEEP-LAYER SHEAR SUFFICIENT FOR SUPERCELLS.
   
   WITH LOW-LEVEL FLOW RELATIVELY WEAK ACROSS THIS AREA PER LOCAL VWP
   DATA...MAIN SEVERE THREAT WILL LIKELY REMAIN LARGE HAIL.  WE WILL
   CONTINUE TO MONITOR THIS REGION...AS MORE WIDESPREAD STORM
   DEVELOPMENT COULD OCCUR OVER THE NEXT COUPLE OF HOURS AND 
   EVENTUALLY WARRANT WW ISSUANCE.
   
   ..GOSS.. 04/18/2009
   
   
   ATTN...WFO...HGX...FWD...CRP...EWX...SJT...
   
   LAT...LON   29810153 30560152 31039899 30349655 28269760 27529950
               28270028 29250078 29810153