The Levoit Core 400S air purifier is on sale at Amazon—quiet, powerful HEPA filtration for wildfire smoke, pollen, and pet dander. Great for medium-sized rooms.

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.