Wildfire smoke updates: CDC issues health alert on wildfire smoke exposure

As Canadian wildfire smoke infiltrates the midwestern United States, 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.

"We recommend children, teens, seniors, people with heart or lung disease, and individuals who are pregnant avoid strenuous activities and limit their time outdoors," Chicago Mayor Brandon Johnson warned in a statement. "For additional precautions, all Chicagoans may also consider wearing masks, limiting their outdoor exposure, moving activities indoors, running air purifiers, and closing windows."

The smoke is forecast to clear on Friday when showers and thunderstorms hit the region.

Earlier this month, the AQI in the northeastern U.S. reached near maximum with levels in the high 400s.

As of Wednesday morning, 20 U.S. states are under air quality alerts from Minnesota down to Georgia and as far north as western New York.

Wildfire smoke from neighboring Canada is currently blanketing large swaths of the United States, from Iowa to western Pennsylvania to North Carolina and most everywhere in between. Only Chicago is getting a small reprieve on Wednesday morning due to a lake breeze, which isn't expected to last for long.

Later on Wednesday, the smoke is expected to cover areas from Minnesota to Washington, D.C. and down to the Carolinas.

By early Thursday morning, the smoke will be seen in Minneapolis, Chicago, Indianapolis, Atlanta and Pittsburgh. But by the afternoon, it will linger from Detroit to Atlanta and east to Washington, D.C. and Philadelphia.

New York City could be impacted as well, but most of the smoke from the Canadian wildfires is expected to stay in western New York state, Pennsylvania and southern New Jersey.