Wednesday Evening Weather Update

Very isolated showers and thunderstorms developed over northern Illinois and southern Wisconsin Wednesday afternoon.  The storms that developed over northern Illinois remained below severe limits, with the exception of the storms near Chicago.  Thunderstorms near Madison and Milwaukee did produce hail and even a tornado northwest of Milwaukee! 


Thunderstorms were quick to intensify over Wisconsin Wednesday because they were closer to an area of low pressure.  Instability was quick to build following thunderstorms Wednesday morning - providing quite a bit of energy in the atmosphere.  But what was lacking over northern Illinois was wind shear - or added spin to help sustain thunderstorms.  That wind shear was higher over Wisconsin where the low pressure system was located.  This allowed storms to rapidly intensify and turn severe.


Same for the storms near Chicago.  There was just enough wind shear in the atmosphere to the east to help build storms up a little more.  Now that a cold front is passing our chance for storms will continue to decrease with skies turning partly cloudy overnight.