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Mesoscale Discussion 672
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   Mesoscale Discussion 0672
   NWS Storm Prediction Center Norman OK
   0201 PM CDT Fri Jun 08 2018

   Areas affected...Portions of eastern Wyoming...western South
   Dakota...and western Nebraska

   Concerning...Severe potential...Watch likely 

   Valid 081901Z - 082100Z

   Probability of Watch Issuance...95 percent

   SUMMARY...Scattered severe thunderstorms are expected to develop
   across parts of the region through this evening, with a primary
   threat of damaging winds and large hail. A couple tornadoes may also
   occur, primarily in southwestern South Dakota. One or more watches
   will be needed within the next two hours or so.

   DISCUSSION...One-minute visible imagery exhibits several fields of
   maturing/towering cumulus across the region this afternoon. The
   primary corridor for more rapid development exists from the Black
   Hills southeastward along a weak surface trough, where satellite and
   radar already have shown a few initial attempts at deep convective
   initiation. An 18Z UNR sounding sampled warm 700mb temperatures
   associated with the base of an EML, currently limiting convective
   growth away from higher terrain. Therefore, initial development
   should remain rooted to the Black Hills. However, gradual
   moistening/cooling aloft will overspread the region from the west
   and increase convective potential at lower elevations through the

   Steep mid-level lapse rates, increasing effective shear, and
   continued heating/moistening of the boundary layer will support a
   primary threat of damaging winds and large hail within a mixture of
   supercell and multicell modes. Additionally, south/southeastward
   propagation east of the Black Hills may yield adequate
   storm-relative helicity for a threat of a couple tornadoes, prior to
   upscale growth by mid evening. 

   This threat over South Dakota will likely necessitate watch issuance
   within the next two hours. Farther west/southwest into Wyoming,
   higher-based convection will gradually intensify as it reaches
   richer boundary-layer moisture with eastward extent, posing a
   damaging wind and large hail threat as well. These cells could be
   covered in the same watch as the SD threat or may be covered in a
   later watch, pending the relative timing of the two threats.

   ..Picca/Grams.. 06/08/2018

   ...Please see for graphic product...


   LAT...LON   43270632 44710662 44950582 45270390 45260269 44860192
               43710133 42340119 41540160 41410183 41270335 41330425
               41520482 42360554 43270632 

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