The Colorado Department of Public Health and Environment issued an air quality advisory Wednesday for most of Western Colorado.

Widespread wildfire smoke, originating largely from out-of-state wildfires, will continue to impact the area. Air quality has been approaching levels where healthy adults may experience serious health effects from prolonged exposure of at least 24 hours, according to the state health department.

The impacted areas include Routt, Moffat, Jackson, Rio Blanco, Grand, Garfield, Eagle, Summit, Mesa, Delta, Pitkin, Lake, Montrose, Gunnison, Chaffee, Saguache, Gilpin, Clear Creek and Park counties.

Heaviest smoke concentrations are expected for north-central and northwestern Colorado along with sheltered valley locations throughout the advisory area. The advisory is in effect until 9 a.m. Thursday.

When moderate to heavy smoke is present, residents are asked to try to remain indoors if possible, especially if they have heart disease, respiratory illnesses, are very young or are elderly. If visibility is less than 5 miles due to smoke, air quality has reached unhealthy levels.