Colorado's famously crystal clear skies appear noticeably less blue this week.

Mike Silverstein, deputy director of the Colorado Air Control Division in Denver, said the haze is caused by smoke from wildfires in Colorado and the West.

Wildfires are burning in Moffat County in northwestern Colorado and near Meeker in Rio Blanco County.

"Because of the fires, there is a lot of fine particulate matter in the air obscuring visibility and exacerbating our usual pollution," Silverstein said.

An additional contributor to the haze, Silverstein noted, is the current temperature inversion over the Front Range. As a result, emissions in the air are trapped until the area gets strong breezes or rain.

The Colorado Department of Public Health and Environment issued an ozone action alert for the Front Range that will be in effect at least until 4 p.m. today. The ozone level is expected to climb past the moderate range through the day. Because particulate levels are likely to rise to the unhealthy-for-sensitive category by this afternoon, people with respiratory or heart problems, the elderly and small children are advised to avoid prolonged exertion outdoors during the next 24 hours.

In Boulder, city and county emergency dispatchers said Thursday they were flooded with calls from residents worried that there was a forest fire burning in the foothills.

lehndorffj@RockyMountainNews.com or 303-954-5103 The Daily Camera contributed.