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

In Chicago, where the Air Quality Index is in the "very unhealthy" category, an Air Quality Alert is in effect until Wednesday night.

Chicago Mayor Brandon Johnson is urging "particularly sensitive populations, including individuals with heart or lung disease, older adults, pregnant people, and young children" to avoid outdoor activities.

Camps have been moved indoors where possible, the mayor said, and he's encouraging "Chicagoans without access to properly ventilated and safe indoor conditions" to "please utilize our public libraries, senior centers, Park District facilities, and the Cultural Center or the six community service centers that operate from 9am-5pm."

President Joe Biden has touched down in Chicago for fundraising and an economic address, and the White House said his schedule has not been modified due to the poor air quality in the city.

"No modifications to today's schedule that I'm aware of as a result of this," principal deputy press secretary Olivia Dalton said. "But certainly, we are monitoring the air quality issues across the country closely and federal agencies are ensuring that federal resources are available in affected regions as appropriate."

The Air Quality Index in hazy Chicago reached 207 on Wednesday morning. Any number over 100 is considered unhealthy for sensitive groups.

-ABC News' Molly Nagle

Wildfire smoke and ash can irritate eyes, nose, throat and lungs, making you cough or wheeze and can make it hard to breathe, according to the U.S. Centers for Disease Control and Prevention.

The CDC says the most effective way to protect yourself during wildfire emergencies is to stay indoors or limit time outdoors when there is smoke in the air. This is especially important for those with heart or lung conditions who are at higher risk for adverse health effects.

"People who are most at risk are [the] elderly, immunocompromised, young children and people who already have respiratory problems, people with asthma and things like that," said Dr. Stephanie Widmer, a member of ABC News' Medical Unit.

Read more here.

-ABC News' Nadine El-Bawab and Youri Benadjaoud

Winds at the mid-levels of the atmosphere are causing the Canadian wildfire smoke to concentrate over a specific area of the midwestern and eastern U.S.

Meanwhile, a heat dome that’s been causing stagnant deadly heat in the Deep South for weeks is keeping the smoke largely out of the region.

The next round of widespread showers and thunderstorms for this area of the eastern Midwest and the East is forecast to arrive on Friday and continue through the weekend, which will clear the smoke.

But as long as the wildfires continue to rage in Canada, these events of dense smoke plumes will likely continue to disperse into the U.S. Canada's wildfire activity typically peaks from June to August.