According to the Greeley Tribune, The Colorado Department of Public Health and Environment has issued an Ozone Action Day alert along the Front Range Urban Corridor, including Weld County, until 4pm today (Friday).

The warning says that "concentrations of ozone will make the air quality unsafe" for adults and children who are active outdoors, and with people who have lung disease. If possible, avoid doing heavy outdoor exertion today or at least until after 4pm.

Source: Greeley Tribune