Millions in the Upper Midwest face the possibility of a severe thunderstorm outbreak Monday—the start of several days of extreme weather threats across the country this week.

Storms with lightning and hail and at least one observed tornado were moving through the upper Midwest on Monday with the potential for strong tornadoes. The National Weather Service said the highest risks — a 4 on a scale of 1 to 5 — were in portions of southern Minnesota,

After days of warnings, storms across Iowa triggered tornado watches and tornado warnings on Monday. What do storm reports say?