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Mesoscale Discussion 806
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   Mesoscale Discussion 0806
   NWS Storm Prediction Center Norman OK
   0222 PM CDT Sun May 21 2017

   Areas affected...Portions of far east TX...LA...and western/central
   MS

   Concerning...Severe potential...Watch unlikely 

   Valid 211922Z - 212115Z

   Probability of Watch Issuance...20 percent

   SUMMARY...Strong to locally damaging winds and perhaps some large
   hail may occur on an isolated basis this afternoon. Watch issuance
   is unlikely.

   DISCUSSION...Thunderstorms have increased in coverage and intensity
   over the past hour or so along a southeastward-moving cold front in
   northern/central LA, and along a sea breeze boundary across southern
   LA. Even through scattered to numerous thunderstorms moved across
   parts of this region yesterday and early this morning, strong
   diurnal heating from mostly sunny skies and a rich low-level airmass
   have allowed for moderate to locally strong instability to redevelop
   as of 19Z. Latest RAP Mesoanalysis indicates MLCAPE has increased to
   around 1500-2500 J/kg along and ahead of the front, as well as along
   the sea breeze boundary, with lapse rates generally 6.5-7.0 C/km in
   the 700-500 mb layer.

   Although low-level winds remain weak, they do strengthen slightly to
   35-40 kt at 500 mb, and veer to westerly with height. Resultant
   effective bulk shear values of 35-45 kt (locally 50 kt) should
   support some updraft organization, and this has been noted in recent
   radar imagery from KDGX/KPOE. There are some indications that a weak
   MCV may have developed in northeastern LA, and convection is
   expected to continue developing along the cold front and then move
   mostly east-southeastward across the discussion area. Isolated
   strong/gusty winds may produce localized damage through this
   afternoon, and the strongest thunderstorm cores may also be capable
   of large hail. Several recent runs of the operational HRRR indicate
   one or more line segments may consolidate along or just ahead of the
   front across portions of southeastern LA and southern/central MS
   over the next several hours. If this were to occur, then the
   damaging wind threat could increase. Still, the overall severe
   weather threat should remain isolated, and watch issuance is
   unlikely.

   ..Gleason/Weiss.. 05/21/2017

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...JAN...LIX...LCH...SHV...

   LAT...LON   30209320 30159389 30189456 30499446 30819376 31319289
               31769240 31969185 32529143 32959111 32949059 32848997
               32498956 31468955 30479026 29949115 30139200 30209320 

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Page last modified: May 21, 2017
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