The weather service office in Lincoln, Illinois, confirmed a tornado struck an area north of the Bryant, a village about 42 miles outside Peoria. Reports of any injuries and damage estimates were unavailable.

The office in Des Moines, Iowa, gave preliminary confirmation of a tornado touching down near Pleasantville, a city of fewer than 2,000 people about 26 miles southeast of Des Moines.

Meteorologist Alexis Jimenez said it would take until at least Wednesday for weather service crews to confirm it.

Multiple tornado warnings, which signify imminent danger, expired for parts of Iowa and Illinois late Tuesday as a segment of the storm front seemed to pass.

For the southern half of the frontal area, the majority of the storms will happen at night, forecasters said. Large hail and winds over 75 mph are possible.

Forecasters said Monday tornadoes as strong as EF2, with sustained winds of 111 mph, could form.

Chicago was under a severe thunderstorm warning as a massive front produced strong winds and large hail. It expired Tuesday afternoon, but it could return in the evening, the weather service said.

The Chicago Fire Department said it responded to at least three reports of roof damage. No injuries were reported, but trees were felled and power poles were also damaged, it said.

At Chicago O’Hare International Airport, 77 departing flights were canceled and 341 were delayed, the flight tracking site FlightAware reported early Tuesday evening.

In western Illinois, a 90 mph gust was recorded in Moline, about 165 miles west of Chicago.

The presence of severe thunderstorm activity doesn’t bode well for the likelihood of tornadoes.

“If they do form,” National Weather Service meteorologist Melissa Byrd said of thunderstorms, “they have the potential for very large-scale and strong tornadoes.”

An estimated 42 million are at risk for severe storms Tuesday, according to NBC News’ weather unit. That grows to around 62 million people Wednesday, as the storm system stretches from northern Michigan to northern Louisiana.

The weather service’s forecast map for Wednesday’s most intense weather has shifted eastward and broadened since Monday. It now encompasses an area east of Dallas and extends northeast along a diagonal swath parallel to the Appalachian Mountains. It reaches Chicago and even parts of New York state.

Cities most likely to get severe weather Wednesday include Chicago; Detroit; Indianapolis; Columbus, Ohio; and Memphis, Tennessee, according to the weather service.

“Potential storm hazards include strong tornadoes, damaging winds, large hail, and locally heavy rainfall and flooding,” the weather service said in an outlook report Tuesday.

Late Tuesday afternoon, the office said a tornado watch had been issued for parts of northern Missouri, western Illinois and eastern Iowa. Severe thunderstorm warnings were in effect for the same region of Missouri.

North and west of the thunderstorm activity, in Wyoming, the Dakotas and Minnesota, the same front was expected to produce blizzard conditions and the possibility of record amounts of snow — as much as 2 feet in places — for April, according to the weather service and the NBC News weather unit.

Many of South Dakota’s state employees worked from home Tuesday under an order from Gov. Kristi Noem, who said the front’s snow and wind would make traveling to workplaces difficult and dangerous. Some highways were being shut down at nightfall as a precaution.

“Citizens should be prepared to stay home if possible,” Noem said in a statement.

Experts say the continental U.S. and the South in particular have the weather misfortune of being where cold fronts from Canada and Pacific storms move south and east and clash with tropical air from the Gulf of Mexico, creating an annual cauldron of stormy weather.

But climate change could be making the extremes worse, resulting in colder cold fronts, stronger tornadoes and bigger hailstones in spring, as well as longer, hotter streaks in summer, they have said.

In mid-March, the National Oceanic and Atmospheric Administration’s spring outlook called for moderate to major flooding from Minneapolis to St. Louis even as drought continued in the northern and central Plains.

“Climate change is driving both wet and dry extremes,” NOAA Administrator Rick Spinrad said in the outlook.

Mirna Alsharif and Kathryn Prociv contributed.