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.

Maps show where new plumes of smoke will cause hazy skies through the end of the week. Low-level smoke is forecast to spread eastward Wednesday across the Appalachians and into the Mid-Atlantic and Northeast.