SPC MESOSCALE DISCUSSION 0834 FOR DEEP SOUTH TEXAS
   CONCERNING...SEVERE THUNDERSTORM POTENTIAL...HEAVY RAINFALL...
   
   VALID 180306Z - 180600Z
   
   VERY LARGE CLUSTER OF STRONG TO SEVERE THUNDERSTORMS WILL CONTINUE
   TO MOVE SOUTHEASTWARD OVER THE NEXT COUPLE OF HOURS.  WHILE THERE
   IS SOME POTENTIAL FOR DAMAGING WINDS WITH THIS ACTIVITY...AND THE
   STORMS ARE ALSO CAPABLE OF PRODUCING RAINFALL RATES IN EXCESS OF 2
   INCHES PER HOURS.
   
   LATEST RADAR COMPOSITE LOOPS SHOW A LARGE CLUSTER OF STRONG TO
   OCCASIONALLY SEVERE THUNDERSTORMS MOVING SOUTHEASTWARD THROUGH
   PARTS OF DEEP SOUTH TEXAS.  SURFACE OBSERVATIONS SHOW THERE IS
   ABUNDANT LOW LEVEL MOISTURE IN PLACE ACROSS THE REGION...WITH
   DEWPOINTS IN THE MID TO UPPER 70S.  THE EVENING SOUNDING FROM
   BROWNSVILLE A MOST UNSTABLE CAPE VALUE IN EXCESS OF 4000 J/KG...BUT
   WET BULB ZERO HEIGHTS ARE NEARLY 13 KFT...INDICATING A SOMEWHAT LOW
   POTENTIAL FOR MORE THAN MARGINALLY SEVERE HAIL.  THE CLUSTER HAS
   CREATED ITS OWN COLD POOL...WHICH SHOULD HELP TO FORCE THE SYSTEM
   TO THE SOUTHEAST...TAKING IT OFF THE LAGUNA MADRE DURING THE NEXT
   2 HOURS OR SO.  RADAR VELOCITY PRODUCTS INDICATE THERE IS A SMALL
   AREA OF FLOW...LIKELY ASSOCIATED WITH THE COLD POOL...IN EXCESS OF
   50 KNOTS JUST OFF THE SURFACE...AND GIVEN THE AMOUNT OF LOW LEVEL
   MOISTURE/INSTABILITY...SOME OF THIS MOMENTUM WILL LIKELY REACH THE
   SURFACE IN THE FORM OF DAMAGING WINDS.
   
   THERE HAVE BEEN A NUMBER OF STORM MERGERS ACROSS THE LOWER VALLEY/
   RIO GRANDE PLAINS TONIGHT.  AS THESE MERGERS OCCUR...THERE HAS BEEN
   SOME ROTATION WITH THE STRONGEST ACTIVITY...BUT AMBIENT WIND SPEEDS
   REMAIN RATHER WEAK...SUGGESTING THE TORNADO POTENTIAL IS NOT
   PARTICULARLY HIGH.  HOWEVER...GIVEN THE AMOUNT OF LOW LEVEL
   MOISTURE IN PLACE...AREAS WHERE THESE MERGERS TAKE PLACE COULD
   RECEIVE VERY HEAVY RAINFALL...WITH THE POTENTIAL FOR MORE THAN 2
   INCHES PER HOUR...AND A BRIEF SPIN-UP COULD OCCUR.
   
   ..REHBEIN.. 05/18/02