A cold front over far northwest Wisconsin and southern Minnesota will move slowly southeast today and tonight. An unstable atmosphere ahead of the approaching cold front will contribute to numerous thunderstorms developing over northern Wisconsin this afternoon. Wind shear in the atmosphere will combine with the instability in producing strong to severe thunderstorms over this part of Wisconsin. Hence more widespread thunderstorms are expected from Green Bay to Wausau, Eau Claire and La Crosse during the evening.
As the front continues to progress southward across southern Wisconsin during the late evening and overnight hours, the thunderstorms are expected to weaken a bit and turn more scattered. The best timing for thunderstorms in the Madison and Milwaukee areas are from 8 pm to 3 am tonight. A few thunderstorms may be strong to severe producing large hail and damaging winds, especially from Fond du Lac southwest to Portage and Baraboo, and north of this line.
Check out where the thunderstorms are now on the regional radars. Click for a larger view.
National Weather Service - Milwaukee/Sullivan