MESOSCALE DISCUSSION 2387
   NWS STORM PREDICTION CENTER NORMAN OK
   0411 AM CST THU DEC 22 2011
   
   AREAS AFFECTED...SRN/CENTRAL LA AND SRN/CENTRAL MS
   
   CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY 
   
   VALID 221011Z - 221045Z
   
   A TORNADO WATCH ISSUANCE IS LIKELY FOR SRN/CENTRAL LA INTO PARTS OF
   SRN/CENTRAL MS WITH THE SEVERE WEATHER THREAT BECOMING A CONCERN
   AROUND OR BY DAYBREAK OVER SWRN LA.  A DEVELOPING NNE-SSW ORIENTED
   SQUALL LINE /WITH EMBEDDED LEWPS AND BOW STRUCTURES/ WILL ADVANCE
   FAIRLY QUICKLY EWD AND SHOULD REACH MCB-LFT AREAS BY 15Z AND INTO
   PIB TO NEW ORLEANS METRO BY 18Z.  DAMAGING WINDS AND ISOLATED
   TORNADOES WILL BE THE PRIMARY THREATS.
   
   SATELLITE IMAGERY SHOWED A DIFFLUENT FLOW REGIME UNDERWAY ACROSS
   MUCH OF CENTRAL/E TX...DOWNSTREAM OF A PROGRESSIVE SHORTWAVE TROUGH
   CURRENTLY MOVING ENEWD THROUGH THE TX BIG BEND REGION.  THIS TROUGH
   HAS BECOME NEUTRALLY ORIENTED...WITH A NEGATIVE TILT EXPECTED THIS
   MORNING AS THE TROUGH AXIS REACHES E TX/LA BY 18Z.  THIS EVOLUTION
   WILL SUPPORT AN INCREASE IN LARGE SCALE ASCENT ACROSS THE DISCUSSION
   AREA...AND A RESPONSE IN LOWER TROPOSPHERIC MASS FIELDS IS ALREADY
   UNDERWAY WITH FURTHER STRENGTHENING OF A SLY LLJ EXPECTED INTO THE
   LOWER MS VALLEY.  SURFACE ANALYSES DURING THE LAST SEVERAL HOURS
   HAVE SHOWN A WARM FRONT ADVANCING NWD...AND AT 0945Z THIS BOUNDARY
   WAS LIKELY LOCATED ALONG OR JUST OFFSHORE OF SERN TX/SWRN LA GIVEN A
   SELY COMPONENT OF OFFSHORE OBS.  A SECOND SURFACE TROUGH EXTENDED
   FROM EXTREME SERN TX NEWD INTO SRN MS TO CENTRAL AL...WITH MODELS
   SUGGESTING THIS LATTER BOUNDARY BECOMES THE PRIMARY SYNOPTIC WARM
   FRONT TODAY.
   
   SURFACE OBSERVATIONS ACROSS CENTRAL-SERN TX AND MESO-ANALYSES
   INDICATED A COLD POOL WAS SUPPORTING A FORWARD PROPAGATING LINE OF
   TSTMS ACROSS E TX TO OFF THE UPPER TX COAST AS OF 10Z.  A SQUALL
   LINE IS EXPECTED TO EVOLVE FROM THIS LINE OF TSTMS AS LARGE SCALE
   ASCENT STRENGTHENS ATOP LOW LEVEL WAA.  BACKED SURFACE WINDS /SELY
   COMPONENT/ ACROSS SRN LA TO SRN MS WILL ENHANCE LOW LEVEL SHEAR TO
   SUPPORT A TORNADO THREAT ACROSS THE WARM SECTOR AS IT SPREADS INLAND
   THIS MORNING AND EMBEDDED WITHIN THE SQUALL LINE.
   
   ..PETERS.. 12/22/2011
   
   
   ATTN...WFO...MOB...JAN...LIX...LCH...SHV...
   
   LAT...LON   29419389 30919318 32379102 33648831 31808849 31158853
               29368947 29129056 29069146 29419389