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Mesoscale Discussion 1257
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   Mesoscale Discussion 1257
   NWS Storm Prediction Center Norman OK
   1219 PM CDT Fri Jul 07 2017

   Areas affected...East-central IL...West-central IN

   Concerning...Severe potential...Severe Thunderstorm Watch likely 

   Valid 071719Z - 071815Z

   Probability of Watch Issuance...80 percent

   SUMMARY...Thunderstorm coverage is expected to increase across
   east-central IL and west-central IN. Some of these storms will
   likely be severe and a watch will be needed across portions of
   region.

   DISCUSSION...Recent surface analysis reveals numerous boundaries
   across the region. The most prominent in terms of convective
   development is the southwestward progressing outflow boundary
   extending from Cook (in far northeast IL) county southeastward into
   central IN and then eastward into central OH. Several strong/severe
   storms developed quickly along this boundary in Lake and Porter
   counties. Intensity of these storms appears to have peaked but
   additional cellular development is possible along this outflow
   boundary with the thermodynamic and kinematic environment supportive
   of strong updrafts capable of hail and damaging downburst winds.
   Another surface boundary in the region is the pre-frontal trough
   extending from Cook county southwestward to just south of PIA and
   continuing southeastward into northeast MO. Development has occurred
   along this boundary in Grundy county with additional development
   possible ahead of this boundary across east-central IL where
   dewpoints in the 70s and cooling mid-level temperatures have
   resulted in no convective inhibition and MLCAPE around 2000 J/kg.

   Overall, thunderstorm coverage is expected to increase in the area
   between the two boundaries mentioned with some of these storms
   capable of large hail and damaging wind gusts. A watch will likely
   be needed to covered this severe weather threat.

   ..Mosier/Grams.. 07/07/2017

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

   ATTN...WFO...LMK...IWX...IND...PAH...LOT...ILX...

   LAT...LON   39868896 41228856 41458788 41468732 40658645 39808574
               38598674 38428847 39868896 

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Page last modified: July 07, 2017
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