Cooler weather will be settling into Wisconsin this week. Below is an animation showing temperatures around 5000 ft (click for larger view) through next Sunday.
Low pressure passing across the region will bring showers on Tuesday, with a chance for showers lingering into Wednesday. Then cooler air will settle into southern Wisconsin Friday and over the weekend.
The increasing liklihood of the colder temperatures will result in a better chance for widespread frost and freezing temperatures over the weekend into early next week.
Maps of the climatological date of median first 32°F and 28°F freeze are shown below:
National Weather Service - Milwaukee/Sullivan, WI