On Saturday, June 20, 2026, the Colorado Department of Public Health and Environment (CDPHE) and the Regional Air Quality Council recorded the highest ozone-related Air Quality Index reading of the day at 112, firmly in the "Unhealthy for Sensitive Groups" category, at 4 p.m. Mountain Standard Time at the CHAT ambient ozone monitor. The Ozone Action Day Alert, which had been issued on Friday, June 19, and extended through midnight Saturday, covered nine Front Range counties: Douglas, Jefferson, Denver, western Arapahoe, western Adams, Broomfield, Boulder, Larimer, and Weld.
This was not a one-day event. CDPHE had already issued a separate Ozone Action Day Alert beginning June 18 for the same Front Range Urban Corridor, warning that "continued hot and stagnant weather will allow ozone to reach the Unhealthy for Sensitive Groups category on Thursday and Friday." The June 20 event represented the third consecutive day of elevated ozone alerts in the region. The primary meteorological drivers — hot, sunny weather with limited cloud cover, stagnant air, and minimal wind to disperse pollutants — are characteristic of Denver's summer ozone season and are expected to intensify as summer 2026 progresses.
