Both Minnesota and Wisconsin were hit by tornadoes during Monday night's severe storms, the National Weather Service confirmed.

Millions in the Upper Midwest face the possibility of a severe thunderstorm outbreak Monday that could bring rounds of dangerous storms capable of unleashing damaging winds, large hail and strong tornadoes — the start of several days of extreme weather threats across the country this week.

Monday is probably the peak, but a storm risk shifts eastward Tuesday. Cities in the highest risk for tornadoes include Minneapolis and Rochester in Minnesota.