Mesoscale Discussion – potential severe storms across northern Illinois

   Mesoscale Discussion 1546
   NWS Storm Prediction Center Norman OK
   0159 PM CDT Sat Jul 20 2019

   Areas affected...Portions of northern 
   Illinois and Chicagoland Area

   Concerning...Severe potential...Watch possible 

   Valid until 4PM CDT...

   Probability of Watch Issuance...40 percent

   SUMMARY...As thunderstorms/outflow near northern Illinois, intense
   convection is possible given the extreme buoyancy in the area.
   Uncertainty remains as to how far south ongoing/newly developing
   convection will push into northern Illinois. A WW is possible should
   convective trends become more clear.

   DISCUSSION...A relatively narrow corridor of undisturbed airmass
   remains in far southern Wisconsin and northern Illinois.
   Temperatures have risen into the upper 80s F to low 90s F with
   dewpoints holding in the upper 70s F. Two ongoing linear segments in
   southwestern and southeastern Wisconsin will likely continue to sag
   slowly southward with time. Given the extreme buoyancy -- MLCAPE of
   4000+ J/kg -- intense convection is possible with damaging winds
   being the primary threat. With the low-level shear vector oriented
   nearly parallel to the outflow, it is uncertain how much development
   will occur southward into Illinois. However, HCRs are currently
   visible on visible satellite imagery in northeastern Illinois. Even
   subtle lift from the outflow boundary may allow parcels to reach
   their LFC. A WW is possible should trends reveal convection is more
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