Strong to severe thunderstorms will be possible for parts of the Midwest, Plains and Northeast on Monday.
The threat of severe weather, which includes damaging winds and possible large hail, could impact Wisconsin, Minnesota, Iowa, Illinois, Missouri, Indiana, Kentucky, Ohio and northwestern Tennessee.
Farther east, Virginia, West Virginia, Maryland, Pennsylvania, New York and Vermont may be affected.
Smoke from Canadian wildfires also will drift towards the Upper Midwest, reducing air quality.
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The heaviest concentrations of smoke are expected in areas that border Lake Michigan.
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Some relief is in store for states that have dealt with extreme heat for weeks as hot temperatures expand eastward towards the Midwest and the Northeast over the next few days.
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As of Wednesday, 253 million Americans will face higher than average temperatures for this time of year.
Fox News’ Greg Norman contributed to this report.