Chicago area, along with much of north and central Illinois and far northwest Indiana, likely to be under a severe thunderstorm watch later this afternoon

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 Mesoscale Discussion 0974
   NWS Storm Prediction Center Norman OK
   1223 PM CDT Sun Jul 01 2018

   Areas affected...Northern and Central Illinois and Far Northwest

   Concerning...Severe potential...Watch likely 

   Valid 011723Z - 011900Z

   Probability of Watch Issuance...80 percent

   SUMMARY...Strong to severe storms are expected this afternoon across
   northern and central Illinois. The primary threat from these storms
   will be damaging wind gusts.

   DISCUSSION...Temperatures have risen into the mid to upper 80s
   across much of Illinois with dewpoints in the upper 70s. This has
   led to MLCAPE around 2500 J/kg. Additional destabilization is
   expected through the afternoon as surface heating continues. Storms
   are expected to form along the cold front (currently in eastern Iowa
   and Eastern Missouri) and move eastward through the afternoon. Flow
   is relatively weak on the ILX 12Z sounding, however, low-level flow
   is forecast to increase to 35 to 40 knots by mid-afternoon. This
   will lead to a marginal shear environment with effective shear
   around 25 to 30 knots with most of this shear focused in the lowest
   1 to 2 km. Nearly parallel orientation of the cold front to the
   deeper level flow will limit a greater severe weather threat,
   however, more robust updrafts could mix down stronger winds, posing
   a damaging wind threat through the afternoon. The threat will be
   maximized with any bowing segments which can orient more normal to
   the low-level flow and accelerate northeastward. A severe
   thunderstorm watch is likely in the next hour or two to cover this
   severe wind threat.
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