The Colorado Department of Health and Environment has issued a health warning across the Front Range due to thick smoke from wildfires in Colorado, Wyoming and Utah.

At 3 p.m., the advisory was extended until 9 p.m.

A cold front bringing air into the state from the north is carrying with it smoke from several large wildfires in Wyoming, said Steve Segin, spokesman for the U.S. Forest Service. To a lesser extent, wildfires in Utah and Colorado are also contributing to the poor air quality.

The 9,085-acre Squirrel Creek fire near Laramie, the 88,000-acre Arapaho fire 28 miles northwest of Wheatland and the 56,000-acre Oil Creek fire near Newcastle are the biggest contributors to the thick smoke, Segin said.

“They’re all fairly big fires,” Segin said. “It’s not too far away.”

He said later in the week with the cold front brings rain, it will get rid of much of the smoke.

“Unfortunately the cold front is not that cold,” Segin said.

The smoke will carry fine particulate concentrations in the moderate to unhealthy range for “sensitive groups” this afternoon and evening, according to a health and environment advisory.

Active children and adults, the elderly, and those with respiratory illnesses such as asthma should reduce prolonged or heavy exertion on Wednesday afternoon and evening, the bulletin says.

“If visibility is less than five miles in smoke in your neighborhood, smoke has reached levels that are unhealthy,” the advisory says.

Kirk Mitchell: 303-954-1206 or kmitchell@denverpost.com