MESOSCALE DISCUSSION 1698
   NWS STORM PREDICTION CENTER NORMAN OK
   1125 AM CDT TUE JUL 28 2009
   
   AREAS AFFECTED...NERN AND PARTS OF ERN TX/NRN LA/FAR SRN AR/PARTS OF
   CENTRAL AND SRN MS
   
   CONCERNING...TORNADO WATCH 630...
   
   VALID 281625Z - 281730Z
   
   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 630 CONTINUES.
   
   A VERY MOIST AIR MASS /PW VALUES 2+ INCHES PER 12Z SOUNDINGS AND
   SURFACE DEWPOINTS IN THE MID-UPPER 70S/ WILL SUPPORT A CONTINUATION
   OF HEAVY RAINFALL RATES /2+ INCHES PER HOUR/ ACROSS PARTS OF ERN TX
   INTO NWRN-NRN LA THROUGH 18Z.  ALTHOUGH OVERALL SEVERE WEATHER
   THREAT APPEARS TO BE DIMINISHING GIVEN WARMING CLOUD TOP
   TEMPERATURES PER IR SATELLITE IMAGERY...SFC-1 KM SHEAR /20-30 KT/
   ALONG 30-40 KT LLJ FROM ERN TX TO NRN LA/CENTRAL MS IS SUFFICIENT
   FOR LOW LEVEL STORM ROTATION.  THESE SHEAR VALUES SUPPORT
   MAINTAINING THE VALID PORTION OF WW 630 UNTIL THE PASSAGE TAKES
   PLACE OF THE NRN LA MESO-LOW AND/OR ESEWD MOVING LINE OF STORMS
   WHICH AT 1615Z EXTENDED FROM JACKSON TO DE SOTO PARISHES.
   
   SURFACE HEATING SOUTH OF THIS MCS WITHIN A VERY MOIST AIR MASS
   /SURFACE DEWPOINTS IN THE MID-UPPER 70S/ IS RESULTING IN AN AXIS OF
   MODERATE INSTABILITY /MLCAPE 2000-2500 J/KG/ EXTENDING FROM SERN TX
   TO SRN MS.  SSWLY LOW LEVEL WINDS ALONG AND S OF THE MCS WILL
   MAINTAIN AN INFLOW OF THE MODERATE INSTABILITY...WHICH COMBINED WITH
   LOW LEVEL WAA BECOMING MORE FOCUSED INTO NERN TX/ ADJACENT
   LA...SUGGESTS ANY NEW TSTMS SHOULD OCCUR ALONG SWRN FLANK OF THE
   MCS.  LOW LEVEL WINDS WILL CONTINUE TO VEER TO WLY IN THE WAKE OF
   THE MESO LOW AS INDICATED BY SHV WSR-88D VAD WITH 35-40 KT VALUES
   SUGGESTING LOCALLY STRONGER WIND GUSTS REMAIN POSSIBLE WITH ANY MORE
   PERSISTENT LINE SEGMENTS.
   
   CLOUDINESS/PRECIPITATION LOCATED DOWNSTREAM ACROSS NERN LA IS
   LIMITING DESTABILIZATION THIS MORNING.  HOWEVER...BREAKS IN THE
   CLOUDS OVER CENTRAL MS SHOULD RESULT IN STRONGER SURFACE HEATING/
   DESTABILIZATION INTO THE AFTERNOON.  FORCING FOR ASCENT ATTENDANT TO
   THE MCV/EMBEDDED MID LEVEL IMPULSE WITH NRN LA MCS MAY SUPPORT
   REGENERATION OF NEW TSTM ACTIVITY THIS AFTERNOON INTO CENTRAL MS
   WITH THE POTENTIAL FOR A NEW WW.
   
   ..PETERS.. 07/28/2009
   
   
   ATTN...WFO...JAN...LIX...LZK...LCH...SHV...
   
   LAT...LON   31329197 31389327 31739346 31879501 32169504 32849501
               32919440 32879361 33439323 33269185 33119051 33128953
               32248928 31298950 31249035 31329197