MESOSCALE DISCUSSION 2128
   NWS STORM PREDICTION CENTER NORMAN OK
   0337 AM CDT MON OCT 22 2007
   
   AREAS AFFECTED...SERN LA EWD ACROSS SRN PARTS OF MS/AL AND THE WRN
   FL PNHDL
   
   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 
   
   VALID 220837Z - 221000Z
   
   POTENTIAL FOR SUPERCELLS CAPABLE OF BRIEF TORNADOES WILL CONTINUE TO
   INCREASE ACROSS DISCUSSION AREA THIS MORNING.  CONVECTIVE TRENDS ARE
   BEING MONITORED FOR A POSSIBLE WW ISSUANCE.
   
   REGIONAL VWPS AND RUC DIAGNOSTIC FIELDS INDICATE THAT A 30-40 KT LLJ
   HAS BECOME ESTABLISHED EARLY THIS MORNING ACROSS THE GULF COAST IN
   RESPONSE TO APPROACHING UPPER TROUGH NOW MOVING INTO THE SRN PLAINS.
   THIS LLJ IS SUPPORTING A CONTINUED NWD TRANSPORT OF AN INCREASINGLY
   MOIST BOUNDARY LAYER THROUGH THE NRN GULF OF MEXICO AND ADJACENT
   GULF COAST WITH DEWPOINTS OF 70-75 F BEING OBSERVED OVER SRN
   LA...FAR SRN MS/AL AND THE WRN FL PNHDL.  THESE OBSERVATIONAL DATA
   SHOW THAT WARM FRONT HAS SHIFTED SLIGHTLY NWD OVER THE PAST SEVERAL
   HOURS...EXTENDING FROM NEAR LCH TO NEAR MSY TO NEAR PNS AS OF 08Z.
   
   IR SATELLITE IMAGERY AND LIGHTNING DATA INDICATE THAT THE MOST
   VIGOROUS CONVECTION EXISTS JUST OFFSHORE SE OF BVE...WITH SHALLOWER
   CONVECTIVE ELEMENTS EXTENDING EWD TO ALONG/S OF THE WRN FL
   PENINSULA.  HOWEVER...THE MOST NOTABLE UPDRAFT ROTATION IS OCCURRING
   WITH THESE SHALLOWER/WARMER CONVECTIVE ELEMENTS FROM SE OF PNS SWD
   INTO THE GULF OF MEXICO.  
   
   CURRENTLY...IT APPEARS THAT THE MARGINAL DEGREE OF INSTABILITY /I.E.
   MLCAPES OF 300-600 J PER KG/ IS LIMITING A MORE SUBSTANTIAL SEVERE
   THREAT ONSHORE.  LATER THIS MORNING...WARM FRONT IS FORECAST TO LIFT
   NWD...SUPPORTING FURTHER AIR MASS DESTABILIZATION INLAND.  THIS
   DECREASING STABILITY COUPLED WITH SUFFICIENTLY STRONG LOW-LEVEL
   SHEAR /0-1 KM SRH OF 150-250 M2 PER S2/ SUGGEST THAT SUPERCELL AND
   INHERENT TORNADO THREAT SHOULD CONTINUE TO INCREASE.
   
   ..MEAD.. 10/22/2007
   
   
   ATTN...WFO...TAE...MOB...JAN...LIX...
   
   29189099 30299018 30938945 31058821 30988726 30958658
   30518603 30208613 29968727 29028898 28829031