Latest SPC Mesoscale discussion hints at possible severe thunderstorm watch into portions of northwest and north central Illinois later this evening

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Mesoscale Discussion 0722
   NWS Storm Prediction Center Norman OK
   0719 PM CDT Mon May 15 2017

   Areas affected...Northern Iowa...southern Wisconsin...and northern

   Concerning...Severe Thunderstorm Watch 214...

   Valid 160019Z - 160115Z

   The severe weather threat for Severe Thunderstorm Watch 214

   SUMMARY...Ongoing severe hail/wind threat should reach the eastern
   portions of WW 214 around 01-02Z.  A downstream severe thunderstorm
   watch will be needed around or before 01Z.  Additional redevelopment
   may occur in western portions of the watch that would pose a hail

   DISCUSSION...Broken linear segments have evolved over north-central
   and northeastern Iowa, with a series of significant hail and wind
   reports primarily owing to hybrid bowing/supercell structures in the
   region.  The convection is propagating eastward at around 30-35
   knots along a remnant outflow/stationary boundary, with a moderately
   unstable pre-convective airmass and sufficient vertical wind shear
   favoring continued organization and a severe threat (potentially
   significant in localized areas) extending east into southern
   Wisconsin and northern Illinois.  A downstream severe thunderstorm
   watch is being considered in these areas and will be coordinated
   soon with affected local forecast offices.

   Farther west, short-term/high-resolution models continue to suggest
   redevelopment of convection in southern Minnesota and northern Iowa
   on the nose of a strengthening low-level jet.  Steep mid-level lapse
   rates will aid in fostering a severe hail threat with this activity
   when it develops and some potential exists for this activity to
   develop in western portions of WW 214.  For this reason, the severe
   threat across the entirety of the WW continues.
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