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Mesoscale Discussion 1271
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   Mesoscale Discussion 1271
   NWS Storm Prediction Center Norman OK
   0910 PM CDT Sun Jul 09 2017

   Areas affected...Portions of central/southern MN and northern IA

   Concerning...Tornado Watch 405...

   Valid 100210Z - 100315Z

   The severe weather threat for Tornado Watch 405 continues.

   SUMMARY...An isolated tornado, large hail, and damaging wind threat
   continues across WW 405. Downstream watch issuance into IA is likely
   by 03Z.

   DISCUSSION...Multiple supercells have developed across
   central/southern MN this evening as large-scale ascent associated
   with a shortwave trough over northern MN overspreads a warm/moist
   low-level airmass. Clouds and earlier convection have limited the
   northeastward return of a strongly unstable airmass across southern
   MN, and a sharp instability gradient extending from northwest to
   southeast is noted across WW 405. VWP from MPX shows a strongly
   veering wind profile supportive of continued maintenance of
   supercell structures in the short term. An isolated tornado threat
   continues with this activity as a low-level jet strengthens this
   evening and effective SRH increases into the 250-350 m2/s2 range. In
   addition, steep mid-level lapse rates, plentiful low-level moisture,
   and 50+ kt of effective bulk shear all suggest a large hail and
   damaging wind threat will persist with these ongoing supercells.
   Some of this large hail may be significant (2+ inches in diameter)
   given MLCAPE in excess of 2000 J/kg along/southwest of the
   instability gradient.

   Upscale growth into one or more small bowing line segments will be
   likely over the next few hours with the strengthening southwesterly
   low-level jet. As supercells transition into mainly a linear mode,
   the primary severe threat should become damaging winds later this
   evening and with southward extent (into southern MN/northern IA).
   Based on latest radar trends, a downstream watch into southeastern
   MN and northern IA will likely be needed by 03Z.

   ..Gleason.. 07/10/2017

   ...Please see for graphic product...


   LAT...LON   45279624 45889504 46069344 44229195 43489137 42799113
               42649206 42549283 42559461 42739494 44259584 45279624 

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