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Mesoscale Discussion 1379
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   Mesoscale Discussion 1379
   NWS Storm Prediction Center Norman OK
   1247 PM CDT Fri Jul 21 2017

   Areas affected...Portions of northeast ND and northwest MN

   Concerning...Severe potential...Watch unlikely 

   Valid 211747Z - 211915Z

   Probability of Watch Issuance...20 percent

   SUMMARY...The area is being monitored for some short-term increase
   in the severe potential. While present indications are that Watch
   issuance will be unlikely through early afternoon, environmental and
   convective trends will continue to be monitored.

   DISCUSSION...Persistent regenerative convection across far northern
   ND -- peripheral to small mid-level perturbations crossing the
   international-border region -- have remained largely elevated above
   a stable boundary layer, thus far. However, with diurnal heating of
   the air mass south of a warm front analyzed as arcing from far
   northeast ND into northwest MN, and given the northward advance of
   this higher theta-e air, there may be some potential for convection
   to begin ingesting parcels originating from surface-based effective
   inflow layers. Despite boundary-layer heating/mixing, surface
   dewpoints are holding in the lower 70s south of this boundary --
   aided by evapotranspiration. This is contributing to around
   1500-2500 J/kg of MLCAPE and limited MLCINH amidst 40-50 kt of
   effective shear.

   These factors may conditionally support some risk for convection to
   become surface based and intensify as supercells. If storm-induced
   hydrodynamic perturbation pressure gradient forces were to
   facilitate storms residing near the warm side of the warm-frontal
   zone, supercell structures with severe hail and wind could evolve --
   given 40-50 kt of effective shear. Backed surface winds near the
   warm front enhancing low-level SRH, and pre-existing vertical
   vorticity near this boundary, could support some tornado risk.
   However, given the modest degree of deep ascent, and substantial
   uncertainty regarding storm-scale dynamics influencing the
   surface-based convective risk -- including the potential for storms
   to remain displaced to the cool side of the boundary -- the severe
   coverage could be limited. However, if it were to appear that a
   greater severe risk were to evolve, Watch issuance probabilities
   could increase.

   ..Cohen/Coniglio/Dial.. 07/21/2017

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

   ATTN...WFO...FGF...

   LAT...LON   47039672 47619745 48539810 48889744 48689613 48229537
               47619520 47179572 47039672 

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Page last modified: July 21, 2017
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