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Mesoscale Discussion 993
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   Mesoscale Discussion 0993
   NWS Storm Prediction Center Norman OK
   1128 AM CDT Mon Jun 12 2017

   Areas affected...Southeast South Dakota...southern
   Minnesota...northern Iowa

   Concerning...Severe potential...Watch likely 

   Valid 121628Z - 121800Z

   Probability of Watch Issuance...80 percent

   SUMMARY...Thunderstorms are expected to increase in coverage and
   intensity through the afternoon hours.  Large hail and potentially
   damaging winds will be the primary threats and a watch is possible
   by 18z.

   DISCUSSION...A cluster of thunderstorms occasionally producing large
   hail was located over southeast South Dakota and southwest Minnesota
   at 1615z.  The storms have thus far been slightly elevated to the
   north of a quasi-stationary frontal boundary that extends from
   central Nebraska northeast along the Minnesota/Iowa border and into
   central/southern Wisconsin.  Temperatures continue to warm to the
   south of the front, and with the nose of a plume of steep mid-level
   lapse rates across the area, strong surfaced-based instability will
   develop this afternoon.  Visible satellite imagery reveals
   increasing cumulus field development along the front as CINH erodes,
   and thunderstorms are likely to increase in coverage/intensity over
   the next few hours within the discussion area. In the presence of
   effective shear generally ranging between 30 and 40 kts, supercells
   and clusters of severe storms will be possible with large hail and
   damaging winds.  Where cold pools can congeal, a more concentrated
   damaging wind threat may develop with east/southeast-moving bowing
   segments. Some tornado risk will exist given the favorable low-level
   SRH near the boundary with the more discrete storms that develop.

   Given the expected increase in storm coverage and severe potential,
   a watch is likely prior to 1730z for the eastern two-thirds of the
   discussion area.

   ..Bunting/Hart.. 06/12/2017

   ...Please see for graphic product...


   LAT...LON   42839358 42899542 42999646 43229705 43469732 43789714
               44069654 44279458 44309312 44259224 44179152 43959075
               43539044 42989076 42779186 42839358 

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