Several states were expected to see dangerously high temperatures until Thursday or Friday, the National Weather Service said Tuesday.
The NWS issued excessive heat warnings for parts of Minnesota, Wisconsin, Indiana, Ohio, Illinois, Missouri and Kentucky.
It also issued warnings about severe thunderstorms in parts of Michigan and South Dakota early Tuesday.
Some 1.5 million people across states hit by thunderstorms last week are still without power, according to Shawn Reynolds of The Weather Channel.
The NWS warned that “people without air conditioning in their home should try to spend at least a portion of each day in an air-conditioned environment” in the coming days as the hot weather continues.
The Weather Channel’s website, weather.com, said the worst heat on July 4 would be located over the central states, with parts of the Midwest seeing highs about 5 to 15 degrees above average.
“The sultry conditions will also extend eastward into the Mid-Atlantic, including Washington, D.C. and Philadelphia, Pa. Be sure to take precautions if you have outdoor plans,” Chris Dolce, of weather.com, said.
Dolce warned that a cold front would bring scattered storms to the Northeast on July 4, saying “a few of these storms could be severe with damaging winds and hail.”
“Parts of the Southeast may deal with pop-up afternoon and evening thunderstorms, particularly in the southern Appalachians and south Florida,” he added.
A second cold front will bring scattered t-storms to the northern Plains and Upper Midwest, from the Dakotas to Minnesota,” Dolce said. “Lastly, an increase in moisture in the Southwest will lead to thunderstorms blossoming during the afternoon and evening in Arizona, New Mexico, southwest Colorado and, perhaps, southern Utah.”