MESOSCALE DISCUSSION 1644
   NWS STORM PREDICTION CENTER NORMAN OK
   0624 PM CDT TUE JUL 21 2009
   
   AREAS AFFECTED...NE TX
   
   CONCERNING...SEVERE THUNDERSTORM WATCH 612...
   
   VALID 212324Z - 220100Z
   
   THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 612
   CONTINUES.
   
   THE NEED FOR A NEW WW IS NOT CURRENTLY ANTICIPATED.
   
   SCATTERED STRONG/SEVERE STORMS HAVE RECENTLY DEVELOPED...GENERALLY
   NORTH/NORTHWEST OF A LINE FROM TYLER TX TO SHREVEPORT LA.  THIS
   APPEARS ON THE WESTERN FRINGE OF FORCING ASSOCIATED WITH A MID-
   LEVEL IMPULSE DIGGING ACROSS ARKANSAS INTO THE NORTHERN GULF
   STATES...WHERE LIFT HAS BECOME JUXTAPOSED WITH STRONGEST HEATING OF
   A MOIST ENVIRONMENT CHARACTERIZED BY LOWER 70S DEW POINTS.  RUC
   GUIDANCE INDICATES THAT MIXED LAYER CAPE IS ON THE ORDER OF 2000-
   3000 J/KG ACROSS THE ARKLATEX...IN THE PRESENCE OF MODERATELY STRONG
   SHEAR BENEATH 30-40 KT NORTHWESTERLY 500 MB FLOW.  AND ISOLATED
   SUPERCELL STRUCTURES COULD CONTINUE TO FORM ANOTHER FEW
   HOURS...BEFORE THE ONSET OF DIURNAL COOLING AND A WARMING/SUBSIDENT
   MID-LEVEL REGIME SUPPRESS ACTIVITY...PERHAPS AS EARLY AS 01-03Z.
   
   ..KERR.. 07/21/2009
   
   
   ATTN...WFO...SHV...FWD...
   
   LAT...LON   32629551 33219515 32989444 32889349 32749282 32519266
               31759445 31969523 32629551