What is a Red Flag Warning?
Red Flag Warnings are issued by the National Weather Service to notify the public and fire agencies in advance of critical weather patterns that may contribute to extreme fire danger and/or extreme fire behavior. A Red Flag Warning is issued for weather events which may contribute to extreme fire behavior and that will occur within 24 hours (or when these conditions are currently being observed). A Fire Weather Watch is issued when weather conditions could exist in the next 12-72 hours. A Red Flag Warning is the highest alert. During these times extreme caution is urged by all residents, because fires are more likely to ignite, and those that do are more likely to spread rapidly and be more difficult to control. A Fire Weather Watch is issued when fire danger is high or when Red Flag Warming conditions are predicted, but not yet observed.
Red Flag Warning conditions are typically related to wind events lasting at least 8 hours when: vegetation is already dry; annual grasses are cured; no rain has occurred in the last 24 hours; and "10-hour" fuels (dead vegetation 1/4 to 1/2 inch in diameter) have less than 6% moisture. Relative humidity and wind speed are the primary factors driving a Red Flag Warning declaration, and must fall into one of the following parameters:
Relative HumidityWind Speed
Day, 29-42% and/or Night, 60-80%30+ mph
Day,19-28% and/or Night, 46-60%21+ mph
Day, 9-18% and/or Night, 31-45%12+ mph
Day, <9% and/or Night, <31%6+ mph
Note that temperature is not a major factor in determining fire danger - hot days do not not trigger a Red Flag Warning unless low humidities and/or sustained, dry winds are also present.
Red Flag Warnings and Fire Weather Watches remain in effect through the expiration time noted in the forecast, or until canceled or upgraded.
How do I know if a Red Flag Warning has been issued?
- Tune into local radio stations
- Check the National Weather Service
- Red Flag Warning Flags posted at the local fire stations as pictured below