Most of Monday looks to be a gorgeous summer-like day with breezy southwest winds and high temperatures in the mid 80's. Most of the afternoon won't be very humid, but late in the afternoon we will notice more humidity arriving ahead of our next storm system.
The heat and higher dew points will then set the stage for strong to severe storms late this afternoon. With the heating of the day, instability will increase and an incoming cold front will help to fire up isolated to widely scattered storms in the area. Storms will initially develop northwest of the Stateline in central Wisconsin and north central Iowa, with storms then moving southeast. Initially storms will be super cellular in nature, with threats of heavy rain, strong winds, large hail, and even a couple of tornadoes.
As the storms move away from the front, they lose the support of the extra lift and instability and I believe will weaken as they move into northern Illinois. By this time the tornado threat will be lower, the Stateline looks to see more of a large hail and heavy rain threat, along with gusty winds. As the forecast stands now, storms won't be moving terribly fast either.
Timing for the Stateline will be around 4pm through about midnight and then drying out overnight.
We will continue to keep you updated as we go through the day.