Air quality in the Upper Midwest region of the U.S. dropped to harmful levels in cities like Chicago and elsewhere in the Great Lakes region, as harmful smoke from persistent wildfires in Canada continued to drift down into that part of the United States.
Meteorologists observed how in less than 24 hours, the Chicago skyline transformed from relatively clear skies on Monday, to a thick brown and gray haze blanketing the city by Tuesday.
In nearby Milwaukee, the air quality index jumped above the 250 mark into the "dangerous" level, reaching an AQI of 266 by Tuesday afternoon.
That "dangerous" marker was applied to localities in Michigan and in northern Indiana, as residents were asked to stay indoors or wear a mask while outside, when possible.
Residents and visitors who are older or suffer from heart or lung disease were asked to be especially cautious until the AQI improved. Chicago health officials asked that people avoid extended time outdoors, and strenuous activity while outside.
Why is Texas so hot right now? A heat dome — and it could grow
Experts say an erratic jet stream has helped stall a lot of hot air over Mexico and Texas.
Chicago Mayor Brandon Johnson said, "As we work to respond to the immediate health concerns in our communities, this concerning episode demonstrates and underscores the harmful impact that the climate crisis is having on our residents, as well as people all over the world."
It has been Canada's worst year for wildfires since it began keeping records on the blazes. In Canada's eastern Quebec province, fires have been burning for weeks.
Meteorologist Jon Erdman, who lives in Wisconsin, said, "I couldn't see a hint of blue sky outside my front door Tuesday morning, and the smoke smell is as strong as I can recall from other Canada smoke episodes in recent years."
The UK's Met Office reported that Canadian wildfire smoke had drifted across the Atlantic and entered UK airspace and on into parts of western Europe.
Experts there said the smoke was staying high up into the atmosphere, which would mostly just change how sunrises and sunsets appeared to those on the ground.
