Wildfire smoke from Canada and northeast Minnesota blanketed much of the Midwest and Northeast for days in mid-July 2026, leading to the highest levels of smoke particulate pollution this century for several cities from Minnesota to Washington, D.C.

(MORE: The Weather Company Labs: active wildfires & fire weather tracker)

This smoke began pouring southward on July 15 from the northern Great Lakes into the Northeast, including Boston, New York City and Toronto.

It then spread and lingered the following 2-3 days over much of the Great Lakes and mid-Atlantic.

New records were smashed

The amount of smoke pollution was the highest since 2014 in Minnesota, according to the Minnesota Pollution Control Agency.

At least 10 metro areas recorded their highest 24-hour averaged air quality index readings from smoke pollution since 1999, according to preliminary data from the Environmental Protection Agency.

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Those included Chicago (511), Cleveland (299), Detroit (490), Milwaukee (414), Pittsburgh (265), the Twin Cities (251) and Washington, D.C. (246). AQI values above 200 are considered very unhealthy by the EPA.

(WATCH: What air quality index forecasts mean)

Cleveland and Detroit had their two highest 24-hour averaged air quality index readings from smoke in 27 years. In many of these cities, these AQI values clobbered previous highs during the late June 2023 smoke event.

On July 16, Detroit, Minneapolis and Chicago were the three most polluted major cities in the world, according to calculations from IQAir.

The thick, acrid smoke was so thick some said they could taste it.

What you need to know to stay safe

Wildfire smoke is hazardous to breathe for several reasons.

It contains microscopic particulate matter much smaller than the width of a human hair that can lodge deep into the lungs and then enter your bloodstream.

It can lead to short-term effects, such as coughing, shortness of breath, a scratchy throat, runny nose and burning eyes.

Prolonged exposure to dense smoke can increase the risk of chronic lung issues and increase inflammation that could lead to heart attacks and strokes.

Check your air quality forecast before heading outside.

You can do that on The Weather Channel app by going to your local forecast, then tapping the "Breathing" button. Or, from your local forecast page on weather.com, click on the "Air Quality" button at the top.

The index is color-coded from green (good) to maroon (hazardous).

If your air quality forecast is....

• At least code orange: More sensitive groups such as those with respiratory or heart conditions, the elderly, children and those pregnant should avoid staying outside more than necessary.
• Code red, purple or maroon: Everyone should limit their time outdoors. Consider exercising indoors and if you need to walk your pet outside, do so as briefly as possible.

(MORE: How air pollution affects you)

Why the smoke?

Plumes of smoke generated by larger wildfires are steered by winds from the ground to the top of the smoke plume.

In the days before this smoke event, triple-digit heat, winds and low humidity triggered a major flare-up of wildfires in Ontario and stirred fires that had been burning since May in northeast Minnesota, prompting a temporary closure of the Boundary Waters Canoe Area and a peacetime emergency declaration from Gov. Tim Walz.

The map below showed locations of over 800 active Canadian wildfires, most numerous from the Northwest Territories to northern Saskatchewan, northern Manitoba, western Ontario, northern Quebec and Labrador.

In this case, the heat dome responsible for the record heat in the northern U.S. was squashed into the Carolinas, setting up a northwesterly wind flow in the upper levels of the atmosphere.

That allowed a pair of cold fronts to sag into the Midwest and Northeast.

Northwest winds behind those fronts tapped smoke from those wildfires not just in western Ontario and northeast Minnesota, but also some lofted smoke from additional fires in northern Canada.

So, while these weaker cold fronts brought relief from heat and humidity, they also piped in wildfire smoke, both aloft and at the ground. This is a scenario that has occurred several past summers this decade and is a pattern we were concerned about during a developing, strengthening El Niño.

(MORE: This $65 DIY air filter builds in just 15 minutes)

Jonathan Erdman is a senior meteorologist at weather.com and has been covering national and international weather since 1996. Extreme and bizarre weather are his favorite topics. Reach out to him on Bluesky, X (formerly Twitter) and Facebook.​