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Mesoscale Discussion 1341
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MD 1341 graphic

   Mesoscale Discussion 1341
   NWS Storm Prediction Center Norman OK
   0322 PM CDT Tue Jul 18 2017

   Areas affected...Portions of eastern MT...northeast WY...western
   SD...southwest ND

   Concerning...Severe potential...Watch unlikely 

   Valid 182022Z - 182245Z

   Probability of Watch Issuance...20 percent

   SUMMARY...A very isolated severe risk could develop later this
   afternoon and persist into the evening. Watch issuance is unlikely,
   though convective and environmental trends will continue to be

   DISCUSSION...Moist upslope flow continues across portions of the
   northern High Plains in a post-frontal air mass. Modest
   boundary-layer moisture is present in this air mass -- e.g., surface
   dewpoints in the lower/middle 50s -- amid efficiently heated higher
   terrain supporting steep low-level lapse rates. As a result, MLCAPE
   around 500-1500 J/kg exists across the discussion area, south of an
   antecedent-convection-reinforced boundary extending from
   east-central MT to north-central SD. The combination of baroclinic
   circulations in proximity to this boundary, orographic ascent over
   the Black Hills vicinity, and deepening boundary-layer circulations
   may support very isolated convective development evolving from
   increasingly agitated cumulus fields noted across portions of the
   area. With around 35-50 kt of effective shear, conditional severe
   hail/wind potential could exist with isolated supercell structures
   advancing southeastward into the evening hours. However, rising
   mid-level heights associated with the lack of large-scale ascent
   suggest that any convection -- if it were to even occur -- would be
   quite isolated.

   ..Cohen/Hart.. 07/18/2017

   ...Please see for graphic product...


   LAT...LON   43770381 44590524 45220611 45990694 46720721 47100676
               47320598 47060497 45310320 44480293 43990307 43800329

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