MESOSCALE DISCUSSION 0519
   NWS STORM PREDICTION CENTER NORMAN OK
   0546 PM CDT SAT APR 18 2009
   
   AREAS AFFECTED...PARTS OF SERN TX / SWRN AND W-CNTRL LA
   
   CONCERNING...TORNADO WATCH 166...
   
   VALID 182246Z - 182345Z
   
   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 166 CONTINUES.
   
   SEVERE THREAT WILL MAINLY BE CONFINED TO IMMEDIATE SERN TX AND SWRN
   LA COAST AND ADJACENT INLAND AREAS FOR THE NEXT FEW HOURS AS BOW
   ECHO MOVES EWD.  HEAVY RAINFALL IS LIKELY ACROSS A LARGE PART OF
   SWRN AND W-CNTRL LA.
   
   22Z SURFACE FIELDS AND RADAR MOSAIC SHOW A PRONOUNCED MESOLOW WITHIN
   COMMA HEAD OF BOW ECHO MOVING EWD ALONG THE EXTREME SERN TX COAST
   INTO SWRN LA.  PRESSURE FALLS WERE NOTED IN ADVANCE OF BOW ECHO OVER
   THE PAST FEW HOURS...INDICATING CONTINUED EWD MCS MOVEMENT TO
   WELL-ORGANIZED STORM COMPLEX.  DESPITE MODEST INSTABILITY DOWNSTREAM
   /AOB 500 J/KG MLCAPE PER OBJECTIVE ANALYSIS/...MOIST LOW LEVEL
   PROFILES AMIDST STRONG LOW LEVEL SHEAR /30 KTS 0-1 KM SHEAR LCH VWP/
   WILL CONTINUE TO SUPPORT THE POTENTIAL FOR AN ISOLD TORNADO OR TWO
   EMBEDDED ALONG LEADING EDGE OR IN COMMA HEAD REGION AS EWD MOVING
   MCS PARALLELS THE SWRN LA COAST.
   
   WITH H25 JET MAX MOVING TOWARDS REGION FROM CNTRL TX THIS
   EVENING...SLY 35 KT 850 JET WILL LIFT NEWD INTO THE LOWER MS RIVER
   VALLEY MAINTAINING MOIST FLUX OF MARITIME TROPICAL AIR
   /CHARACTERIZED BY 1.75+ INCH PWAT ACCORDING TO GOES SOUNDER DATA/
   INTO REGION.  THIS WILL CONTINUE TO SUPPORT HEAVY RAINFALL POTENTIAL
   ACROSS A LARGE PART OF CNTRL AND SWRN LA THE NEXT FEW HOURS.
   
   ..SMITH.. 04/18/2009
   
   
   ATTN...WFO...LCH...SHV...HGX...
   
   LAT...LON   29689462 30759445 31419434 31789426 31919413 31939349
               31919254 31829224 30899236 30069250 29619267 29599322
               29599414 29619431 29689462