Canadian wildfire smoke is triggering air quality alerts across the U.S. Midwest and Northeast on Thursday, as the northern nation’s boreal forests continue to burn at a rate not seen except for a historic season in 2023.

Smoke has made its way back into the northern tier of the U.S., prompting air quality alerts in North Dakota, Minnesota and Montana on Wednesday and Thursday.

Smoke from Canadian wildfires is engulfing much of the eastern and central United States and and is expected to continue for days.