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 date this year. Changing with the prevailing weather patterns, smoke from those fires has repeatedly been pushed southward over the U.S. from the Great Plains to the Northeast this summer.
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READ MORE: How to Protect Yourself from Smoky Wildfire Air
Winds from the northwest are currently sending that smoke southeast, straight into the midwestern U.S., Dye says. That’s bringing the region cool temperatures and low humidity, but a high-pressure air mass is keeping local wind speeds too low to clear the smoke.
Meteorologists expect conditions in the Midwest to clear up on August 2 and particularly on August 3, Dye says, although the smoke will head eastward into northern New York State and Michigan over the weekend.
Wildfire smoke is one of several sources of a type of air pollution called PM2.5, fine particulate matter in which the particles are no larger than 2.5 microns wide. These tiny particles are especially dangerous because they can infiltrate deep into the lungs and beyond. Exposure to PM2.5 pollution has been linked to respiratory issues but also cardiovascular and metabolic conditions and cancer.
You can check your local air quality on the Environmental Protection Agency’s AirNow website and on some weather apps. Conditions are measured on a 500-point scale called the Air Quality Index. On this index, small numbers represent healthier conditions and large numbers represent high risk.
READ MORE: How to Use the Air Quality Index
Any AQI measurement above 200 poses increased risks to everyone. Numbers above 150 indicate some risk to the general public; those above 50 indicate some risk to people who are sensitive to air pollution, including the very young, the very old, and people with asthma or heart or lung disease.
When air quality is bad, you can protect yourself by running air filters inside and wearing an N95 mask outside.
