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Mesoscale Discussion 1270
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   Mesoscale Discussion 1270
   NWS Storm Prediction Center Norman OK
   0357 PM CDT Sun Jul 09 2017

   Areas affected...extreme northeast South Dakota...central and
   southern Minnesota and far western Wisconsin

   Concerning...Severe potential...Watch likely 

   Valid 092057Z - 092230Z

   Probability of Watch Issuance...95 percent

   SUMMARY...Thunderstorms are expected to develop by 22-23Z across
   central MN and possibly as far west as northeast south Dakota and
   rapidly become severe. Supercells capable of very large hail will be
   the initial primary threat, but gradually transitioning to damaging
   wind into the evening. A couple of tornadoes are also possible.

   DISCUSSION...Broken mid-level clouds associated with lead shortwave
   trough are finally beginning to diminish from the west. This process
   is promoting greater boundary layer destabilization from eastern
   south Dakota into southwest MN. Latest objective analysis shows a
   corridor of 2500 J/KG MLCAPE south and west of a weakening outflow
   boundary that extends across southern MN to a weak low in northeast
   SD. A quasi-stationary front extends from the surface low eastward
   through central MN, and a cold front stretches westward from the
   surface low along the ND/SD border.

   An upstream shortwave trough is moving southeast into northern MN
   and will be accompanied by an increase in frontogenetic forcing near
   and east of triple point from northeast SD into central MN.
   Thunderstorms are expected to initiate in this zone by 22-23Z. A 50
   kt mid-level jet accompanying this feature is resulting in 50+ kt
   0-6 km shear with discrete supercells likely to be the initial storm
   mode. These storms will be capable of producing very large hail,
   isolated wind damaging and possibly a couple of tornadoes. Later
   this evening, a strengthening westerly low-level jet will promote
   evolution to a forward propagating MCS with an increasing threat for
   damaging wind.

   ..Dial/Weiss.. 07/09/2017

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

   ATTN...WFO...ARX...MPX...FGF...FSD...ABR...

   LAT...LON   44339545 45379747 46079668 46269543 45459291 44769219
               43779259 43789407 44339545 

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Page last modified: July 09, 2017
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