Tornado warnings have been issued for parts of Minnesota as multiple rounds of severe thunderstorms are expected across the central U.S. on Monday, some capable of producing damaging winds, large hailstones and strong tornadoes, forecasters say.

“Tornadoes, some possibly strong (EF2 or greater damage), as well as damaging hail and high winds, are all possible threats,” Weather.com senior digital meteorologist Chris Dolce said. “There is some uncertainty in this forecast, with the biggest unknown being how widespread the storms will be.”

According to the National Weather Service, the region most at risk for severe weather stretches from Iowa to Wisconsin, including major cities Des Moines, Iowa, and Minneapolis and St. Paul, Minn.

When are the storms expected to arrive?

“The most dangerous period is likely during the late afternoon and evening, when strong tornado potential should be maximized,” the weather service said.

A tornado watch was issued for parts of parts of Iowa, Minnesota and South Dakota until 8 p.m. CT. At around 3 p.m. CT, a tornado warning was issued for Stearns and Wright counties in Minnesota. When a watch refers to conditions that are potentially severe development, while a warning signifies that severe weather has started or is imminent, according to the National Weather Service.

The weather service’s Storm Prediction Center has put the risk of severe storms in the Twin Cities area at a level 4 out of 5, with tornadoes, “widespread hail up to the size of apples” and damaging winds likely.

National Weather Service Storm Prediction Center

The city of Minneapolis issued an alert urging residents to be prepared to seek shelter immediately if a tornado warning is issued.

“Regardless of the risk level, an episode of dangerous weather is likely today, with all hazards possible,” the NWS Twin Cities office said.

‘Multiday outbreak’

The system is part of a “multiday outbreak” of severe storms that could affect tens of millions of Americans from the southern Plains to the Northeast, according to Accuweather.

On Tuesday, the threat of severe weather will shift east, with portions of the Ohio Valley and Northeast at risk of large hailstones, damaging winds and isolated tornadoes. Among the cities that could see serious impacts: Buffalo, Cincinnati, Cleveland, Detroit and Pittsburgh.

National Weather Service Storm Prediction Center

On Wednesday, a second system capable of producing severe weather will enter the Plains, with millions of people from northern Texas to southern Missouri bracing for large hailstones, damaging winds and tornadoes.

Flash flooding is also possible as rounds of storms are expected to bring heavy rain, with up to 5 inches of rain predicted in some areas.