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.