Millions of Americans across the Midwest, Northeast and swathes of the South and Southwest have been are under air quality alerts Monday after smoke from multiple wildfires blanketed much of the U.S.

Tuesday night is when the high pressure system shifts to the east, the NWS says. This should allow south winds to return, which should usher out the smoke. But then it will bring on more heat and humidity. So get ready to turn your AC back on.