Smoke from wildfires blazing across Canada is once again wafting over huge portions of the U.S. Midwest and worsening air quality there. On August 1 conditions are particularly bad in Minnesota, Iowa and Illinois.

“If you take a look at visible satellite imagery , you can even see it’s just this kind of milky, hazy setup,” says Melissa Dye, a meteorologist at the National Weather Service’s Twin Cities office in Minnesota. “It’s almost like it’s foggy out,” she says of conditions on the ground in Minneapolis and Saint Paul.

So far this year, Canada has seen more than 3,000 fires burn more than 22,000 square miles. The nation’s forest fire center was monitoring more than 300 fires as of July 23, the latest data available. Among Canada’s provinces, Alberta has seen the most fires to dat

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