Mesoscale Discussion – Possible Severe Thunderstorm Watch issuance later this Wednesday morning east of Chicago

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Mesoscale Discussion 0895
   NWS Storm Prediction Center Norman OK
   0844 AM CDT Wed Jun 10 2020

   Areas affected...northern IN...southwest and western Lower MI

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

   Valid 101344Z - 101515Z

   Probability of Watch Issuance...80 percent

   SUMMARY...Storms will gradually intensify this morning and likely
   require a severe thunderstorm watch issuance by 11am-12pm EDT.  Max
   thunderstorm gust potential will initially range 45-60 mph but
   strengthen into the 50-70 mph range towards midday as both the
   magnitude/coverage of damaging gusts increases.

   DISCUSSION...Radar mosaic shows a developing band of storms from
   east-central IL to the Chicago south side with another cluster of
   storms developing over northwest IN expected to move into southwest
   Lower MI during the next 1-2 hours.  Visible-satellite imagery shows
   cloud streets across northern IN into southern Lower MI, indicative
   of a very moist boundary layer.  Specifically regarding moisture,
   the 6am EDT Detroit, MI observed sounding showed a 16.3 g/kg lowest
   100mb mean mixing ratio, a climatological maximum through June 15th
   during the period of record (since 1949).  

   Pockets of strong heating per cloud breaks will contribute to a
   moderately unstable airmass by mid-late morning with little to any
   remaining convective inhibition as temperatures warm into the
   low-mid 80s.  KIWX and KGRR show 30-40 kt in the 1-2 km AGL layer
   with 50 kt around 3km AGL at KGRR.  As the mid-level migratory
   shortwave trough approaches the Great Lakes from MO today,
   additional storm development/strengthening is expected.  As a
   result, damaging gusts will become more common as bands of storms
   intensify through the late morning and into the early afternoon.  A
   tornado or two cannot be ruled out given the moist boundary layer
   and adequate speed shear in the lowest 1-2 km, but the general
   unidirectional southerly wind profile will tend to favor damaging
   gusts as the primary severe hazard.


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