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Mesoscale Discussion 925
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   Mesoscale Discussion 0925
   NWS Storm Prediction Center Norman OK
   1100 AM CDT Wed May 31 2017

   Areas affected...Extreme southeast Louisiana to Gulf coastal
   counties of southeast MS and southwest AL

   Concerning...Severe potential...Watch unlikely 

   Valid 311600Z - 311830Z

   Probability of Watch Issuance...5 percent

   SUMMARY...A locally greater, though marginal coverage, tornado risk
   is possible today across extreme southeast Louisiana into the Gulf
   coastal counties in southeast MS and southwest AL.  WW issuance is
   unlikely due to spatiotemporal limitations in this region, and given
   that a somewhat greater potential appears for stronger rotational
   couplets to remain offshore as waterspouts.

   DISCUSSION...Trends in mosaic reflectivity and velocity data across
   extreme southeast LA (primarily including St. Bernard Parish)
   indicated a few thunderstorms with periodic, and occasionally
   persistent, low-level rotational couplets moving to the
   north-northeast toward the islands off of the southeast MS coast
   (including Cat Island).  General weakening of these couplets
   occurred as they tracked closer to the coast, while recent radar
   imagery showed these storms have shifted more toward the east, with
   additional storms developing near buoy 42040 and tracking toward the

   15Z RAP suggested some increase in surface-3 km CAPE today (to
   around 100 J/kg) and surface vorticity to be persistent near a weak
   west-east oriented boundary located near or just offshore the coast
   of southeast MS and southwest AL.  Storms developing and/or
   interacting with this boundary could have enhanced potential for
   low-level rotation, while background vertically veering low-midlevel
   winds (per WSR-88D VWP data) also support rotating storms.  A very
   rich boundary layer (precipitable water around 1.6 inches per 12Z
   LIX sounding and mean mixing ratios around 15 g/kg) and moderate
   instability should prove favorable for additional storm development
   through the afternoon.

   ..Peters/Hart.. 05/31/2017

   ...Please see for graphic product...


   LAT...LON   29388985 30368938 30578905 30678863 30658810 30458777
               30158761 29308785 29008812 28918866 28888920 28998957

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