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.

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

The first severe thunderstorm warning of the day in Minnesota has been issued, with the NWS Sioux Falls saying the warning is in effect in Beaver Creek in southwestern Minnesota, where 2-inch size hail is possible. It has now expanded to three Minnesota counties.