A significant cold front is sweeping through the Midwest and Northeast, prompting freeze warnings for millions across 19 states. The National Weather Service has issued warnings in places like northeastern Wisconsin, Milwaukee, and various counties in Ohio, predicting temperatures could plunge by as much as 30 degrees within hours. Many areas, including the Chicago region, are bracing for their first frost of the season, with temperatures expected to drop into the 20s. While some areas will experience unseasonable cold and potential frost tonight, warmer weather is anticipated to return by the weekend.