MESOSCALE DISCUSSION 2252
   NWS STORM PREDICTION CENTER NORMAN OK
   1128 AM CDT THU SEP 23 2004
   
   AREAS AFFECTED...PORTIONS SRN LA
   
   CONCERNING...SEVERE TSTM POTENTIAL - T.S. IVAN TORNADOES 
   
   VALID 231628Z - 231930Z
   
   POTENTIAL FOR A FEW SUPERCELLS AND ASSOCIATED BRIEF TORNADOES IS
   EXPECTED TO INCREASE GRADUALLY THROUGH EARLY-MID AFTERNOON AS
   BOUNDARY LAYER CONTINUES TO HEAT/DESTABILIZE...HELPING TO INCREASE
   CONVECTIVE COVERAGE IN CORRIDOR OF FAVORABLE LOW LEVEL VERTICAL
   SHEAR. AREA WILL BE MONITORED FOR PSBL WW.
   
   STRENGTHENING/EXPANDING BAND OF CONVECTION -- EVIDENT AT 16Z FROM
   NEAR ARA SEWD OVER ST MARY/WRN TERREBONNE PARISHES THEN SWD OVER
   GULF -- SHOULD SHIFT WWD ACROSS DISCUSSION AREA AND APPEARS TO 
   REPRESENT LARGEST PROBABILITIES ON MESO-BETA SCALE.  MODIFIED LIX
   RAOB AND RUC/ETA FCST SOUNDINGS SUGGEST MLCAPES 1000-1500 J/KG
   POSSIBLE AS SFC TEMPS WARM INTO LOW-MID 80S F...IN RELATIVELY CLOUD
   FREE AREAS BETWEEN EXISTING CLOUD/PRECIP BANDS.  ASSOCIATED
   DIFFERENTIAL HEATING BOUNDARIES MAY SERVE TO ENHANCE LOW LEVEL
   CONVERGENCE/SHEAR/VORTICITY AND POTENTIAL FOR ROTATION IN ANY
   SUSTAINED CONVECTION WITH WHICH THEY INTERACT. AFOREMENTIONED
   SOUNDINGS AND VWP DATA SHOW WEAK MIDLEVEL FLOW -- I.E. 500 MB WINDS
   AROUND 10 KT -- THOUGH NARROW CORRIDOR OF STRONGER MIDLEVEL WINDS IS
   LIKELY OVER COASTAL SWRN LA WHERE NO OBSERVATIONAL SAMPLING IS
   PRESENT.  HOWEVER...EXPECT ENLARGED LOW LEVEL HODOGRAPHS -- WITH 0-1
   KM SRH UP TO NEAR 300 J/KG -- JUXTAPOSED WITH WEAKENING CINH AND
   INCREASING BUOYANCY.  LCH VWP SHOWS HODOGRAPH EXPANDING WITH TIME
   AND THIS TREND SHOULD CONTINUE THROUGH AT LEAST MIDAFTERNOON AS
   CENTER OF IVAN PASSES S AND SW OF THAT LOCATION.
   
   REF NHC ADVISORIES -- I.E. WMO HEADER WTNT24 KNHC -- FOR LATEST
   INFORMATION REGARDING TRACK/INTENSITY GUIDANCE AND TROPICAL
   WATCHES/WARNINGS FOR IVAN.
   
   ..EDWARDS.. 09/23/2004
   
   
   ATTN...WFO...LIX...LCH...
   
   29749314 29939327 30419353 30709344 30889313 30899292
   30829250 30469143 30069099 29579078 29139070 28889067
   28759071 28739098 28809120 28979150 29499266 29649297