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Mesoscale Discussion 1800
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MD 1800 graphic

   Mesoscale Discussion 1800
   NWS Storm Prediction Center Norman OK
   0618 AM CST Wed Dec 20 2017

   Areas affected...Part of south-central and southeast MS and adjacent
   parishes of southeast LA

   Concerning...Severe potential...Watch unlikely 

   Valid 201218Z - 201445Z

   Probability of Watch Issuance...20 percent

   SUMMARY...A Marginal threat for a tornado or damaging wind gust is
   possible this morning across part of south-central to southeast
   Mississippi, and adjacent parishes of southeast LA.

   DISCUSSION...Trends in water-vapor imagery indicated the OK
   shortwave trough has moved into AR as it weakened some in amplitude.
   This trough will progress east this morning into the Mid South,
   while the attendant surface low shifts across northern MS into
   northern AL.  Given the track of the midlevel trough, the deep-layer
   shear vectors with southward extent are expected to remain westerly
   through the morning.  This vector orientation across the
   eastward-advancing cold front and lack of stronger forcing for
   ascent within the warm sector suggests storm mode will remain
   cellular as convection moves east of the lower MS Valley.

   Strong deep-layer shear and backed southerly surface winds across
   southeast LA and southern MS will sustain long hodographs with
   low-level curvature.  These kinematics, despite weak buoyancy,
   suggest a Marginal risk for a tornado or damaging wind gust cannot
   be ruled out this morning, primarily across south-central and
   southeast MS, and perhaps into adjacent parishes of southeast LA.

   ..Peters/Thompson.. 12/20/2017

   ...Please see for graphic product...


   LAT...LON   30789084 31499012 32118929 32218849 31278842 30838856
               30518938 30508989 30539049 30619088 30789084 

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