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Mesoscale Discussion 1074
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   Mesoscale Discussion 1074
   NWS Storm Prediction Center Norman OK
   0817 PM CDT Sat Jun 17 2017

   Areas affected...Northern and central Illinois...northeastern
   Missouri...and far southeastern Iowa

   Concerning...Severe Thunderstorm Watch 345...

   Valid 180117Z - 180215Z

   The severe weather threat for Severe Thunderstorm Watch 345

   SUMMARY...The severe threat continues across WW 345.

   DISCUSSION...Scattered to numerous thunderstorms have evolved this
   afternoon along/just ahead of a surface boundary along northwestern
   portions of WW 345.  A few supercell structures have evolved along
   with broken linear segments.  The severe threat should continue with
   this activity as it migrates/propagates southeastward over the next
   few hours - greatest in western and central portions of the watch
   where instability is the strongest.  A severe threat will exist into
   northeastern Illinois, although a couple of factors are in play that
   may affect the severe threat over the next couple of hours: 1)
   somewhat weaker instability with northeastward extent, which may
   mitigate the severe threat (as confirmed by recent radar/lightning
   presentation of the storms) and 2) a gradual increase in low-level
   wind fields over the next couple of hours, and 3) remnant low-level
   outflow boundaries, which may result in a brief, localized uptick of
   severe activity especially if updrafts can interact with these

   With time, activity will continue to migrate southeastward into
   central Illinois with a continued hail and wind threat - especially
   as low-level flow increases and ascent from an amplifying mid-level
   trough over Minnesota approaches.  Downstream areas (eastern
   Illinois and western Indiana) may experience an increasing severe
   threat in the next 1-3 hours in response to current activity near
   Peoria.  Additionally, significant hail may occur in western
   Illinois and northeastern Missouri, especially with storms that can
   exhibit stronger updraft rotation.

   ..Cook.. 06/18/2017

   ...Please see for graphic product...


   LAT...LON   40449292 41009188 41499066 42398922 42498822 42108765
               41248697 40708672 40328671 39998694 39618722 39368803
               39358894 39628980 39599113 39459198 39689266 40099295

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