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Mesoscale Discussion 475
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   MESOSCALE DISCUSSION 0475
   NWS STORM PREDICTION CENTER NORMAN OK
   1202 PM CDT TUE APR 29 2014

   AREAS AFFECTED...PORTIONS OF NERN AND SERN LA / MUCH OF SRN AND
   CNTRL MS

   CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY 

   VALID 291702Z - 291830Z

   PROBABILITY OF WATCH ISSUANCE...95 PERCENT

   SUMMARY...THUNDERSTORM INITIATION IS FORECAST WITHIN THE NEXT HOUR
   OR TWO.  RAPID SEVERE STORM DEVELOPMENT WILL OCCUR THIS AFTERNOON
   AND A TORNADIC SUPERCELL THREAT WILL LIKELY ENSUE AS STORMS MATURE.

   DISCUSSION...RECENT SURFACE MESOANALYSIS PLACES A COLD FRONT OVER
   PARTS OF THE LOWER MS RIVER VALLEY EXTENDING SWWD INTO THE UPPER TX
   COASTAL PLAIN.  AN ARCING OUTFLOW BOUNDARY FROM A PRIOR MCS
   --CURRENTLY OVER THE NERN GULF OF MEXICO-- IS DRAPED FROM NEAR THE
   MOUTH OF THE MS RIVER INTO FAR SWRN MS.  THE AIRMASS TO THE S AND W
   OF THE OUTFLOW BOUNDARY IS BECOMING QUITE UNSTABLE WITH AN AGITATED
   CU FIELD DEVELOPING OVER MUCH OF LA AND STRONG HEATING OCCURRING
   OVER MUCH OF MS.  AS LOW-LEVEL MOISTURE ADVANCES NWD ON THE BACKSIDE
   OF THE OUTFLOW BOUNDARY...MODERATE TO STRONG /1500-2500 J PER KG
   MLCAPE/ DESTABILIZATION IS EXPECTED.  

   AS ASCENT PROVIDED BY A 130 KT JET STREAK AND BOUNDARY LAYER
   HEATING/MOISTENING OCCUR...THUNDERSTORMS ARE FORECAST TO DEVELOP
   FIRST NEAR THE MS RIVER AND SPREAD EWD THIS AFTERNOON THROUGH MS AND
   EVENTUALLY INTO AL.  STRONG DEEP-LAYER FLOW FIELDS WILL STRONGLY
   FAVOR SUPERCELLULAR STORM MODES AND A FORECAST STRENGTHENING IN H85
   FLOW /30-40 KT/ THIS AFTERNOON INTO THIS EVENING WILL BOOST
   LOW-LEVEL SHEAR AND CONCURRENTLY SUPPORT AN INCREASE IN TORNADO
   POTENTIAL.  GIVEN THIS SCENARIO...LONGER-LIVED SUPERCELLS CAPABLE OF
   TORNADOES /SOME POSSIBLY STRONG/ AND A LARGE TO VERY LARGE HAIL
   THREAT IS PROBABLE.

   ..SMITH/THOMPSON.. 04/29/2014


   ATTN...WFO...MOB...MEG...JAN...LIX...LCH...

   LAT...LON   32429166 33599031 33928952 33748879 33378847 32238869
               31308902 30788951 30469043 30549152 31199197 32429166 

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Page last modified: April 29, 2014
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