Sunny summer days may not be quite as bright this year as smoke from wildfires burning across Canada occasionally spreads across the United States, resulting in hazy conditions and poor air quality.

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.

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.