A smoky haze wafted over parts of western Colorado on Thursday and Friday from wildfires burning in and around the state.

The smoke is mainly from the Turner Gulch Fire in Mesa County and the Dragon Bravo Fire burning near the Grand Canyon in Arizona, according to the Colorado Department of Public Health and Environment’s smoke blog.

The smoke impacts led officials to issue an air quality health advisory for Mesa County, where the Turner Gulch Fire has burned on 17,747 acres, according to InciWeb.Wildfire.gov. Currently the largest wildfire burning in Colorado, the Turner Gulch Fire was 41% contained as of Thursday morning.

While wildfire smoke was worst in the vicinity of the Turner Gulch Fire, areas of northwest Colorado — including towns along the Interstate 70 corridor — experienced moderate air quality impacts Thursday, according to PurpleAir.com‘s air quality map.

As upper-level winds change direction heading into the weekend, the areas of Colorado seeing smoke may shift and it is possible more smoke could move to counties north and east of Mesa County, according to the Colorado Smoke Blog.

“Smoke may linger in areas where it has infiltrated already, and additional smoke may arrive, depending on transport winds and fire activity on Thursday,” the smoke blog states. “Daytime mixing of the atmosphere will play a role on how quickly smoke may dissipate.”