Air Quality Advisory Extended In Metro Denver, Boulder

The Front Range saw a break from ozone and wildfire smoke warnings over the weekend, but by Wednesday, air quality had diminished. An air quality advisory has been extended until Thursday at 4 p.m.

Smoke has flowed into the region from out-of-state wildfires and the worst concentrations are expected along the I-25 corridor from Denver to Fort Collins, according to the Colorado Department of Public Health and Environment.

Most of Denver's metro area is under the 'unhealthy for sensitive groups' air quality rating, but regions north of Denver could reach the 'unhealthy' category, public health officials said.

Visibility is expected to be 'poor' or 'extremely poor.'

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Ozone concentrations are expected to be in the 'good to moderate range' Thursday, so unusually sensitive people should consider reducing prolonged or heavy outdoor exertion. Fine particular matter concentrations are also expected to be in the 'unhealthy for sensitive groups' or 'unhealthy' range Thursday.

Carbon monoxide and nitrogen dioxide levels are expected to remain in the 'good' category Thursday, health officials said.

Dry, warm conditions are expected to spread smoke from the Middle Fork fire near Steamboat Springs and the massive Cameron Peak wildfire in Larimer County.

>> Read the full air quality advisory here.