Canadian wildfire smoke back in Midwest for second straight year. Will it hit Illinois?

Smoke from Canadian wildfires has prompted health warnings across the Upper Midwest for the second year in a row -- and Illinois could be hit next.

Fires raging in British Columbia and Alberta have filled the skies with haze over parts of Montana, the Dakotas, Minnesota and Wisconsin on Sunday, lingering into Monday morning.

Unhealthy air pollution levels mean everyone in Minnesota should stay indoors and avoid heavy exertion outdoors, the Minnesota Pollution Control Agency said in its first statewide air quality alert of the season Sunday. Scheduled to end at noon Monday, the advisory was extended until 11 p.m. for southern Minnesota including the Twin Cities metro area.

The Wisconsin Department of Natural Resources said the air quality was unhealthy for sensitive people in multiple counties across the state's northern two-thirds on Sunday. Set to end at noon Monday, the advisories were kept in place until midnight.

Michigan's Upper Peninsula was also under hazy skies Monday. Some people reported the smell of smoke, said Joe Phillips, a National Weather Service meteorologist in Marquette, Michigan.

What to know for Illinois

Prevailing winds could send the smoke south and east as far as Iowa and Chicago, leaving skies looking milky by late Tuesday or early Wednesday, said Rafal Ogorek, a meteorologist in the National Weather Service’s Chicago office. Most of the smoke was expected to linger over Minnesota, Wisconsin and northern Michigan, hanging between a mile and 2 miles above the ground.

According to the NBC 5 Storm Team, winds could bring the smoke to the Chicago area over the next few days, but the big question will be whether that smoke aloft will mix down to the surface and spark air quality alerts similar to ones seen in Minnesota and Wisconsin.

As of 4 p.m. CT, Chicago's air quality was listed as "unhealthy," with a PM2.5 of 159. PM2.5 is an air pollutant also known as fine particulate matter.

• To check the air quality level in your area right now, click here.

"Wildfire smoke is expected to move into Northern Illinois later this evening and linger over parts of Illinois through [May 14]," the government website AirNow reported.

In total, there are six categories for air quality: green, or good; yellow, or moderate; orange, or unhealthy for sensitive groups; red, or unhealthy; purple, or very unhealthy; and maroon, or hazardous.

"Some members of the general public may experience health effects; members of sensitive groups may experience more serious health effects," the "unhealthy" category description states.

Daily AQI Color	Levels of Concern	Values of Index	Description of Air Quality
Green	Good	0 to 50	Air quality is satisfactory, and air pollution poses little or no risk.
Yellow	Moderate	51 to 100	Air quality is acceptable. However, there may be a risk for some people, particularly those who are unusually sensitive to air pollution.
Orange	Unhealthy for Sensitive Groups	101 to 150	Members of sensitive groups may experience health effects. The general public is less likely to be affected.
Red	Unhealthy	151 to 200	Some members of the general public may experience health effects; members of sensitive groups may experience more serious health effects.
Purple	Very Unhealthy	201 to 300	Health alert: The risk of health effects is increased for everyone.
Maroon	Hazardous	301 and higher	Health warning of emergency conditions: everyone is more likely to be affected.

What to know about Canada wildfires

A record number of wildfires in 2023 forced more than 235,000 people across Canada to evacuate and sent thick smoke into parts of the U.S., prompting hazy skies and health advisories in multiple U.S. cities.

There were 200 fires burning in Canada by mid-May last year, compared with 90 fires as of this Sunday, said Dave Phillips, senior climatologist at Environment and Climate Change Canada, a government environmental protection agency. A fire raging near Fort Nelson in British Columbia’s far northeastern corner has forced evacuations.

The chances of more wildfires this summer appear high. Lightning strikes could trigger fires that quickly spread in forests suffering intense drought in northeastern British Columbia, northwestern Alberta and the southern Northwest Territories, according the Canadian National Wildland Fire Situation report.

An analysis by World Weather Attribution, an initiative that aims to quickly evaluate the role of climate change in the aftermath of extreme weather events, found climate change more than doubled the chances of hot, dry weather that helped fuel the fire season.

Loretta Mickley, co-leader of Harvard University's Atmospheric Chemistry Modeling Group, said her group did papers in 2013 and 2015 looking at fire activity and ecosystems with an eye toward the future. She said increasing fire activity is consistent with a warming climate.

Drought conditions look to be less severe in Ontario and Quebec in the coming months, but temperatures are expected to be higher than normal, and it's difficult to predict if the moisture will cancel out the heat, she said.

“What will happen this summer? It depends on what the meteorology is like today and what happened over the winter,” she said. “In some regions a lot of rain in winter led to abundant vegetation. If that is followed by dryness or a drought then all that vegetation is ready to be burnt up and provide fuel to the fires.”

If Canada does see a repeat of last year's fire season, it's far from clear if the U.S. will get haze on the scale of 2023. Fires in Quebec and Ontario produced most of the smoke that enveloped The Eastern U.S. — but those regions rarely see such large fires. Instead of pushing the smoke west, the wind drove it south, covering the eastern quarter of the U.S. from the Mississippi River Valley to Manhattan with haze.

“It was an unfortunate, odd kind of weather pattern where you had winds encouraging that air to come south and then east,” said Phillips, of the Canadian environmental protection agency. “And it was just a shock to meteorologists, to the world and to everyone who had to endure it ... I think it will be a fraction of a concern as it was last year.”