Greg Perkins [KC9GHZ]

The Storm Prediction Center has placed far northern Illinois and southern Wisconsin in a slight risk area for severe thunderstorms.  The main threats appear to be large hail and a few damaging wind gusts.  A cold front has stalled out over northern Illinois, stretching back across Iowa to a low pressure center in South Dakota.  A few relatively high-based storms should develop along the cool side of the surface front in advance of the surface low by late afternoon or early evening.  These storms should propagate eastward.  Vertical wind shear will be the strongest on the cool side of the front, where a few supercells may develop.  It appears that the severe threat will be mainly north of the Lake County area.

There is another chance of thunderstorms on Tuesday.  It currently looks like the greatest instability will be in the area around 1:00 PM.  These storms will be largely surface-based and driven by atmospheric heating, so they should wind down by around sunset as the surface temperatures start to drop.  The instability won’t be very strong, so at the moment it doesn’t look like we should see anything terribly powerful and the storms probably won’t breach severe limits.  For the weather geeks among you, I’ve attached a forecast sounding from the NAM model at the bottom of this post.

I’ll be posting another update late tonight once the new model runs are in.