On a comparatively quiet day for Colorado wildfires, blazes raging to the north in Wyoming covered the northern Front Range with smoke and haze, worrying residents and leading officials to issue a health advisory.

The Colorado Department of Public Health and Environment issued a health warning until 9 p.m. Wednesday, saying particulates were in the moderate-to-unhealthy range for “sensitive groups.” The Department on Thursday issued an ozone action alert until 4 p.m. saying concentrations were in the moderate to unhealthy-for-sensitive groups range.

Active children and adults, the elderly and those with respiratory illnesses were warned against prolonged or heavy exertion.

A cold front bringing air into the state from the north carried 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 were 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 that later in the week, the cold front will bring conditions that will clear up much of the smoke.

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

Meanwhile, in Colorado Springs, nearly a half-inch of rain was a welcome respite Tuesday night for firefighters accustomed to triple-digit temperatures while fighting the Waldo Canyon fire.

Just after 4 p.m., an average of four-tenths of an inch of rain fell on the 18,247-acre fire that destroyed 347 homes since it began June 23.

“It’s not going to put it out, but it is going to cool it down considerably,” Tim Johnson, fire spokesman, said Wednesday.

But Johnson added that rain can be a double-edged sword, particularly if too much rain falls at once after a wildfire.

“It could knock the fire down, but it could contribute to flooding also,” he said.

On Wednesday night, officials said the fire was 90 percent contained and expected it would be fully contained by Friday.