hazy Denver sky
Cars drive down Colfax Ave during rush hour while smoke from the Black Forest fire in Colorado Springs flows through downtown Denver on Wednesday, June 12, 2013. (Grant Hindsley, The Denver Post)

The thick, fire-fed haze over parts of Colorado poses risks for people with breathing conditions, the Colorado Department of Public Health and Environment warned, adding that the smoky skies were expected to linger until at least Thursday morning.

As Wednesday wore on, Denver's view of the mountains was obscured, the sky looked like winter and the smell of smoke was inescapable.

Ozone-concentration levels were in the "moderate" to "unhealthy for sensitive groups" range on Wednesday afternoon, especially in the foothills from the south and southwest suburbs of Denver north to Fort Collins, according to the health department.

"If you can see or smell smoke, it is a good indicator to reduce your exposure by going indoors," Jill Law, El Paso County's public health director, said in a statement.