Canadian wildfire smoke is infiltrating the Midwest on Tuesday and the air in Chicago has deteriorated to the Air Quality Index's "very unhealthy" category.
The AQI in hazy Chicago reached 250 on Tuesday afternoon. Any number over 100 is considered unhealthy for sensitive groups.
MORE: Canada breaks record for annual wildfire smoke emissions: CopernicusChicago Mayor Brandon Johnson warned in a statement Tuesday, "We recommend children, teens, seniors, people with heart or lung disease, and individuals who are pregnant avoid strenuous activities and limit their time outdoors. For additional precautions, all Chicagoans may also consider wearing masks, limiting their outdoor exposure, moving activities indoors, running air purifiers, and closing windows."
The worst air quality in the world Tuesday morning was in Wisconsin.
The state's Department of Natural Resources issued a statewide air quality advisory that's in effect until Thursday.
MORE: Wildfire smoke map: Forecast shows which US cities, states are being impacted by Canadian wildfiresOn Tuesday afternoon the AQI in Milwaukee registered in the "very unhealthy" category.
"The most significant air quality and health impacts are anticipated between noon on Tuesday, 6/27 and noon on Wednesday, 6/28," Wisconsin's Department of Natural Resources said. "This is a dynamic situation, and conditions may change rapidly over the next few days. It is important to pay close attention to the air quality in your area and take action, especially if you don’t feel well."
By Tuesday evening the densest smoke will be in cities including Springfield, Illinois; Peoria, Illinois; Louisville, Kentucky and Roanoke, Virginia.
On Wednesday morning, the haze will be noticeable from Iowa to North Carolina. The smoke is forecast to be strongest in cities near Cedar Rapids, Iowa, and St. Louis, Missouri.
On Wednesday afternoon, the smoke will start to weaken slightly but reduced air quality is still expected from Minnesota to North Carolina.
Even the Northeast could see an impact. New York City Mayor Eric Adams warned that New Yorkers could experience worse air quality on Wednesday and New York Gov. Kathy Hochul said air quality health advisories have been issued for several upstate New York regions.
The smoke is expected to lessen significantly Wednesday night into Thursday. A milky sky is still expected from Michigan to Georgia and those with asthma and other respiratory issues may still have difficulty breathing.
The smoke is forecast to clear on Friday when showers and thunderstorms hit the region.
Earlier this month the Canadian wildfire smoke drifted toward the Northeast, blanketing New York City, Philadelphia and Washington, D.C., in a dangerous orange haze and prompting serious air quality alerts in over a dozen states. On June 7 New York City's AQI hit 484, the highest level on record.