MESOSCALE DISCUSSION 0021
   NWS STORM PREDICTION CENTER NORMAN OK
   1033 PM CST SAT JAN 12 2013
   
   AREAS AFFECTED...PORTIONS E TX...WRN/NRN LA...EXTREME SRN AR.
   
   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 
   
   VALID 130433Z - 130600Z
   
   PROBABILITY OF WATCH ISSUANCE...40 PERCENT
   
   SUMMARY...CONVECTION IS GROWING IN COVERAGE/INTENSITY OVER
   PREFRONTAL WARM SECTOR IN E TX.  GIVEN STRENGTH OF AMBIENT WIND
   FIELDS AND SHEAR PROFILES...ANY SUSTAINED WARM-SECTOR CONVECTION MAY
   OFFER RISK OF DAMAGING GUSTS AND A FEW TORNADOES...WHETHER FROM
   SUPERCELLS OR CIRCULATIONS EMBEDDED IN QUASI-LINEAR SEGMENTS. 
   ADDITIONAL WW MAY BE REQUIRED IF CURRENT INCREASING TRENDS CONTINUE.
   
   DISCUSSION...SFC MESOANALYSIS SHOWS SOMEWHAT WAVY ARCTIC COLD FRONT
   FROM NERN AR SWWD THROUGH LIT AREA TO CADDO PARISH LA...BASICALLY
   BISECTING WW 3...THEN SWWD ACROSS PANOLA AND HOUSTON COUNTIES TX TO
   MIDDLE TX COASTAL PLAIN.  FRONT WILL PROCEED SEWD ACROSS MOST OF
   DISCUSSION AREA THROUGH 09Z.  THIS BOUNDARY IS SHARPLY DEFINED AND
   STG...UNDERCUTTING CONVECTION DEVELOPING ALONG OR IMMEDIATELY AHEAD
   OF IT.  THIS PROCESS SHOULD QUICKLY HALT SVR WIND AND TORNADO
   POTENTIAL WITH SUCH ACTIVITY.  HOWEVER...MODIFIED SHV/LCH RAOBS
   SUGGEST MINIMAL MLCINH OVER WARM SECTOR IN EXTREME E TX AND
   LA...ALONG WITH 500-1000 J/KG MLCAPE.  LOW-LEVEL MOISTURE TRANSPORT
   AND WAA SHOULD OFFSET/RESTRICT PACE OF DIABATIC SFC COOLING ENOUGH
   TO KEEP EFFECTIVE LIFTED PARCELS ROOTED AT OR VERY NEAR SFC FOR
   SEVERAL MORE HOURS.  LLJ MAY DIMINISH WITH TIME AFTER 06Z...BUT
   STILL SHOULD CONTRIBUTE TO ENLARGED HODOGRAPHS THROUGH MOST OF
   PRE-DAWN HOURS.  AS SUCH...SLY-SSELY SFC WINDS BENEATH LLJ SHOULD
   RENDER EFFECTIVE SRH VALUES 250-500 J/KG OVER MUCH OF THIS
   AREA...WITH ONLY GRADUAL SFC VEERING EXPECTED OVERNIGHT. 
   MEANWHILE...DEEP-LAYER SHEAR SHOULD REMAIN FAVORABLE FOR ORGANIZED
   SVR...E.G. EFFECTIVE SHEAR MAGNITUDES 55-65 KT OVER MOST OF
   PREFRONTAL AIR MASS.
   
   ..EDWARDS/COHEN.. 01/13/2013
   
   
   ATTN...WFO...JAN...LZK...LCH...SHV...HGX...
   
   LAT...LON   30979522 32729408 33699285 33689161 33469126 32229161
               31009301 30879455 30979522