MESOSCALE DISCUSSION 0485
   NWS STORM PREDICTION CENTER NORMAN OK
   0556 PM CDT THU APR 16 2009
   
   AREAS AFFECTED...TX SOUTH PLAINS AND LOW ROLLING PLAINS SWD INTO THE
   PERMIAN BASIN AND CONCHO VALLEY
   
   CONCERNING...TORNADO WATCH 157...
   
   VALID 162256Z - 170030Z
   
   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 157 CONTINUES.
   
   THROUGH 00Z...THE GREATEST THREAT FOR TORNADOES WILL EXIST WITH ANY
   MATURE SUPERCELLS CROSSING OUTFLOW BOUNDARY FROM HOCKLEY AND LYNN
   COUNTIES SEWD THROUGH BORDEN...HOWARD INTO STERLING COUNTIES. 
   OTHERWISE...EXPECT LARGE HAIL TO BE THE PRIMARY SEVERE WEATHER
   THREAT WITH THE MOST INTENSE STORMS.
   
   SYNTHESIS OF LATEST VISIBLE SATELLITE...RADAR AND SURFACE
   OBSERVATIONAL DATA INDICATES A WELL-DEFINED OUTFLOW BOUNDARY SLOWLY
   SHIFTING WWD THROUGH THE TX S PLAINS AND PERMIAN BASIN...WITH THIS
   FEATURE EXTENDING FROM LAMB AND HOCKLEY COUNTIES SEWD THROUGH DAWSON
   AND MARTIN INTO STERLING COUNTIES AS OF 2245Z.  SEVERAL STORMS HAVE
   RAPIDLY EVOLVED INTO SUPERCELLS WHILE CROSSING THIS BOUNDARY WITH
   THE MOST INTENSE STORMS LOCATED OVER LUBBOCK...GARZA AND INTO BORDEN
   COUNTIES...ON THE IMMEDIATE COOL SIDE OF THIS BOUNDARY.
   
   MODIFICATION OF RUC PROXIMITY SOUNDINGS FOR COOLER BOUNDARY LAYER
   CONDITIONS N/E OF OUTFLOW BOUNDARY STILL YIELDS A MODERATELY
   UNSTABLE AIR MASS /MLCAPE OF 1000-1200 J PER KG/ WITH LCL HEIGHTS
   AROUND 1 KM.  THIS THERMODYNAMIC ENVIRONMENT COUPLED WITH LOCALLY
   BACKED SURFACE WINDS AND RESULTANT RATHER STRONG LOW-LEVEL SHEAR
   /I.E. 0-1 KM SHEAR OF AROUND 20 KT PER LBB VWP/ WILL CONTINUE TO
   SUPPORT STRONG SUPERCELLS WITH A THREAT OF TORNADOES.  THIS TORNADO
   THREAT IS LIKELY CONFINED A 50-70 KM CORRIDOR NE OF OUTFLOW BOUNDARY
   WITH SURFACE-BASED INSTABILITY DECREASING WITH EWD EXTENT DUE TO
   COOLER/DRIER BOUNDARY LAYER CONDITIONS.
   
   OTHERWISE...EXPECT CONSIDERABLE HAIL PRODUCTION WITH THE MOST
   INTENSE STORMS...SOME THAT MAY APPROACH 2 INCHES IN DIAMETER.
   
   ..MEAD.. 04/16/2009
   
   
   ATTN...WFO...OUN...SJT...LUB...AMA...MAF...
   
   LAT...LON   32930317 33040286 34690269 34870139 34789982 32829985
               30970046 30880129 30910261 32170324 32930317