Wildfire smoke temporarily improves, more coming this week

Wildfire smoke from Canada and northeast Minnesota will continue to sweep over parts of the Midwest and East this weekend leading to dangerous air quality, and another round after that could plunge into parts of the South in the week ahead.

Here are the latest smoke forecasts

Air quality alerts have been issued for parts of the Midwest, as well as parts of Upstate New York.

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

This weekend

There is some short-term good news.

Showers and thunderstorms that swept through the Ohio Valley and Northeast on Saturday should help to temporarily clean the air of smoke particles in some areas.

But another round of smoke will dive southward into the western Great Lakes on Sunday, then sweep into the Ohio Valley and could impact at least parts of the Northeast and mid-Atlantic.

The week ahead

Unfortunately, model forecasts suggest a third round of smoke could nosedive southward through the upper Midwest beginning Tuesday, sweep into the Northeast around Wednesday, but could also nose-dive into parts of the South Wednesday and Thursday.

When it started

This latest smoke event began Wednesday from the northern Great Lakes into the Northeast, including Boston, New York City and Toronto.

It then spread Thursday and lingered into Friday over much of the Great Lakes and mid-Atlantic. Cities such as Cleveland, Columbus, Detroit, Pittsburgh and Washington, D.C. have reported code purple “very unhealthy” air quality Friday, according to the EPA’s air quality index.

(WATCH: What air quality index forecasts mean)

Late Thursday morning, Detroit, Minneapolis and Chicago were the three most polluted major cities in the world, according to calculations from IQAir. However, the smoke has thinned and air quality improved considerably Friday in parts of the upper Midwest, including the Twin Cities.

(MORE: Wildfire smoke tracker maps)

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.

If you’re in these affected areas in the Midwest and Northeast, 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.

Last Monday, triple-digit heat, winds and low humidity triggered a major flare-up of wildfires 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 shows locations of 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 recent 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 will allow a pair of cold fronts to sag into the Midwest and Northeast.

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

So, while these weaker cold fronts bring relief from heat and humidity, they may also usher in some 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 this summer 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.​