As many as 87 million people, from eastern Montana to Manhattan, are under slight risk for severe weather on Tuesday, the National Weather Service's Storm Prediction Center said.
Damaging wind, hail and few tornadoes are expected on the High Plains, while severe thunderstorms could stretch from Michigan and Indiana to the Northeast.
The forecast comes a day after twin tornadoes devastated Nebraska, killing at least two and critically injuring 16.
Earlier Tuesday, a tornado watch was issued for an area that included Chicago and Milwaukee, The Weather Channel's Justin Abraham reported.