People in northeastern Montana were advised Wednesday to limit their time outdoors as smoke from Canadian wildfires worsened air quality to unhealthy levels.

Air quality at the Sidney and Glendive stations in northeastern Montana was unhealthy, with air quality indexes of 190 and 193, respectively, according to a Montana Department of Environmental Quality (MTDEQ) webpage. Unhealthy air quality levels occur when the AQI is between 151 and 200.

Once the air quality reaches 201 or higher, the air quality is considered “very unhealthy” and “the risk of health effects is increased for everyone,” according to the MTDEQ. Hazardous air quality occurs at an AQI of 301 or higher.

The poor air quality comes after the National Weather Service (NWS) office in Glasgow, Montana, issued a dense smoke warning, which will remain in effect until 6 p.m. local time on Wednesday. High winds were also reported, which also prompted a wind warning for the lake.

“Smoke from wildfires can have health implications. Strong winds and rough waves on nearby lakes create hazardous conditions for small craft,” the advisory said.

In a post on X (formerly Twitter), NWS Glasgow reported that the smoke had cleared by Wednesday evening.

“Smoke from wildfires has overtaken northeastern Montana and some locations are currently experiencing 1 to 3 miles of visibility reduction,” the message said“This will lead to poor air quality, but the smoke will clear as a cold front moves from north to south this afternoon/evening.”

The NWS Glasgow home page advised people not to burn debris and to keep their windows closed. People were also advised not to burn candles as this could contribute to indoor pollution.

Smoke prompted meteorologists to issue air quality warnings for western Montana earlier this week as smoke from wildfires gathered in that part of the state, NWS meteorologist Luke Robinson said at the time. Newsweek that the smoke was caused by local fires, while the smoke in northeastern Montana came from Canadian fires.

As of Wednesday afternoon, most of the MTDEQ air quality monitoring stations in western Montana reported moderate air quality levels, with the station in Hamilton reporting levels that are “unhealthy for sensitive groups.”

Regarding the approaching cold front, NWS Chief Meteorologist Richard Maliawco said Newsweek that temperatures in northeastern Montana will drop 5 degrees from the highs in the 70s and low 80s on Wednesday. Winds will increase Wednesday night, with gusts up to 30 mph, and that will push smoke out of the Glasgow forecast region, he said.

Maliawco warned that given the behavior of the wildfires, smog and smoke could return by the weekend.