Minnesota has issued an air quality alert for the entire state until Monday evening. The state’s northern counties are expected to see air quality that is considered unhealthy based on the Environmental Protection Agency’s Air Quality Index (AQI), which measures daily air pollution. Under these conditions, even people who aren’t part of a sensitive group may experience health effects like itchy eyes, runny noses, coughing or shortness of breath.

Wisconsin issued an air quality advisory on Friday that expired the next day, but the state’s Department of Natural Resources said another advisory could be warranted by Sunday afternoon. Northwestern counties will likely see heavy smoke on Sunday evening, the department said, and it could migrate across the state on Monday. Many parts of Wisconsin could experience air quality that’s unhealthy for sensitive groups, with a pocket of even poorer air quality in the northwest.

In parts of North Dakota, the air quality currently meets the AQI’s “very unhealthy” threshold, meaning all those exposed have an increased risk of health effects. State officials have urged residents, particularly those with respiratory conditions, to consider limiting their outdoor activities if it’s smoky where they live. Other ways to reduce exposure include closing windows, running indoor air filters and wearing an N95 mask outside.

South Dakota also issued an air quality alert for certain areas that lasts through Sunday or until conditions improve.

Wildfire smoke can travel hundreds or thousands of miles, posing health risks to people far away from an active blaze.

In 2023, smoke from Canadian wildfires turned skies orange in the Northeastern U.S. and led to unhealthy air quality levels in New York City, Boston, Philadelphia and Washington, D.C.

A study last year found that people who inhaled the smoke in New York and New Jersey were likely exposed to extremely large concentrations of fine particulate matter — tiny particles in the air that can penetrate deep into the lungs. Short-term exposure to these particles can increase the risk of cardiac arrest, asthma attacks or stroke, while long-term exposure can increase the risk of heart disease, lung cancer and chronic kidney disease.

Wildfires are becoming more frequent and intense due to climate change, along with other extreme weather events like hurricanes and heat waves.

As smoke from Canada billowed into the Midwest over the weekend, severe storms swept through the South and East Coast and millions of people in the West were under heat alerts, with temperatures climbing past 100 degrees.