Red Flag Warning

Locations Affected

Aurora, CO ∙ Denver, CO ∙ Fort Collins, CO ∙ Lakewood, CO ∙ Thornton, CO ∙ Centennial, CO ∙ Westminster, CO ∙ Boulder, CO ∙ Arvada, CO ∙ Greeley, CO

Headline

...THIS IS A PARTICULARLY DANGEROUS SITUATION FOR IN AND IMMEDIATELY ADJACENT TO THE FOOTHILLS, BETWEEN 5500 AND 9000 FEET, FOR BOULDER AND JEFFERSON COUNTIES ON FRIDAY...
Strong west winds, sustained 45-55 mph with gusts upwards of 85-105 mph, are expected in the foothills of Boulder and Jefferson Counties beginning early Friday morning. Relative humidity values are expected to drop into the low teens, possibly upper single digits. While Red Flag conditions, critical fire weather, are expected across a larger area in northern Colorado, the most extreme conditions are expected to be along Highway 93 from Jefferson County into Boulder County and along US-36 north of Boulder to the Larimer County line and westward. There will be a high potential for fast moving wildfires, should any new starts occur.
Winds toward I-25 and eastward will be slower to develop, and also speeds will be considerably lighter. That said, gusts of 25-40 mph are still expected to combine with very low humidity and cured grasses to support critical fire weather conditions. Areas farther east into eastern Adams, Arapahoe, Elbert, and Lincoln counties have more uncertainty if those winds even develop, so those locations remain under a Fire Weather Watch.
Such conditions may be a longer duration than usual, with potential for low humidity to extend well into the evening hours.

Full Alert Message

URGENT - FIRE WEATHER MESSAGE National Weather Service Denver/Boulder CO 508 PM MST Thu Dec 18 2025 ...THIS IS A PARTICULARLY DANGEROUS SITUATION FOR IN AND IMMEDIATELY ADJACENT TO THE FOOTHILLS, BETWEEN 5500 AND 9000 FEET, FOR BOULDER AND JEFFERSON COUNTIES ON FRIDAY... Strong west winds, sustained 45-55 mph with gusts upwards of 85-105 mph, are expected in the foothills of Boulder and Jefferson Counties beginning early Friday morning. Relative humidity values are expected to drop into the low teens, possibly upper single digits. While Red Flag conditions, critical fire weather, are expected across a larger area in northern Colorado, the most extreme conditions are expected to be along Highway 93 from Jefferson County into Boulder County and along US-36 north of Boulder to the Larimer County line and westward. There will be a high potential for fast moving wildfires, should any new starts occur. Winds toward I-25 and eastward will be slower to develop, and also speeds will be considerably lighter. That said, gusts of 25-40 mph are still expected to combine with very low humidity and cured grasses to support critical fire weather conditions. Areas farther east into eastern Adams, Arapahoe, Elbert, and Lincoln counties have more uncertainty if those winds even develop, so those locations remain under a Fire Weather Watch. Such conditions may be a longer duration than usual, with potential for low humidity to extend well into the evening hours. ...RED FLAG WARNING FOR A PARTICULARLY DANGEROUS SITUATION REMAINS IN EFFECT FROM 10 AM FRIDAY TO MIDNIGHT MST FRIDAY NIGHT FOR WIND AND LOW RELATIVE HUMIDITY FOR ABOVE 5500 FEET IMMEDIATELY ADJACENT TO THE FOOTHILLS OF BOULDER AND JEFFERSON COUNTIES... * AFFECTED AREA...Fire Weather Zone 239. * TIMING...From 10 AM Friday to midnight MST Friday night. * WINDS...West 30 to 40 mph with gusts up to 80 mph or more immediately next to the foothills. * RELATIVE HUMIDITY...As low as 8 percent. * IMPACTS...Conditions will be favorable for rapid fire spread. Avoid outdoor burning and any activity that may produce a spark and start a wildfire. PRECAUTIONARY/PREPAREDNESS ACTIONS... This is a Particularly Dangerous Situation that poses a significant threat to life and property in the event of a wildfire start. Residents are urged to assemble an emergency supply kit and know their evacuation routes. In some cases, safe and timely evacuation may not be possible should a fire approach. Have multiple ways to receive instructions from emergency services, and evacuate if ordered to or if a fire threatens.

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