Red Flag Fire Weather Restrictions
What Is a Red Flag Warning?
Red Flag Warning events are defined by critical weather and fire danger conditions that could lead to extensive wildfire occurrences and/or control problems on existing wildfires or prescribed burns.
When Is a Red Flag Warning Issued?
A Red Flag Warning is issued by the National Weather Service when there is high confidence that Red Flag criteria will be met within the next 24 to 48 hours or when those criteria are already being met or exceeded. A warning may be issued for all, or portions of, a fire weather zone or region.
Are Fire Restrictions Applied During a Red Flag Warning?
Yes. There is now automatic implementation of Stage 1 Fire Restrictions for all of unincorporated Jefferson County whenever the National Weather Service issues a Red Flag Warning for all or part of Jefferson County. These restrictions are known as Red Flag Fire Weather Restrictions and will be posted on Twitter at https://twitter.com/jeffcosheriffco whenever they are in effect.
How Long Will Red Flag Fire Weather Restrictions Last?
The Red Flag Fire Weather Restrictions will be in effect from the time the Red Flag Warning is in effect until the end of the day the Red Flag Warning is in effect, at 11:59pm.
If a Red Flag Warning is in effect for longer than a day, the fire restrictions will remain in effect until 11:59 p.m. on the last day of the Red Flag Warning period.
What Criteria Determines a Red Flag Warning?
Red Flag Warning Criteria – A combination of weather and fuels conditions (as determined by fire management) for any 3 hours or more in a 12 hour period. These criteria for the forecast area of the Denver/Boulder NWS office are defined as the following:
- Frequent gusts of 25 mph or greater – AND relative humidity of 15% or less
- Dry thunderstorms (15% coverage or more, constituting an LAL 6.)
In addition to the basic criteria above, a combination of other elements may result in Red Flag conditions:
- Haines Index of 5 or 6, indicating a moderate or high potential for large, plume-dominated fire growth.
- Wind shifts associated with frontal passages.
- First significant lightning event (wet or dry) after an extended hot and dry period.
- Poor relative humidity recovery overnight (RH remains at 40% or lower.)
- In the forecaster's judgment, any combination of weather and fuel moisture conditions would cause extensive wildfire occurrences.
Red Flag Watch – High potential for the development of Red Flag criteria (see above) in the next 12-72 hours. A watch may be issued for all or portions of a fire weather zone or region. Zones impacted by the event will be listed within the Red Flag Warning (Local NWS-issued Watches, Warnings, and/or Advisories can be accessed at: weather.gov/bou/JeffersonCounty).