A term used by fire-weather forecasters to call attention to limited weather conditions of particular importance that may result in extreme burning conditions. It is used when it is an on-going event or the fire weather forecaster has a high degree of confidence that Red Flag criteria will occur within 24 hours of issuance.
Red Flag criteria occurs whenever a geographical area has been in a dry spell for a week or two, or for a shorter period. If before spring green-up or after fall color, and the National Fire Danger Rating System (NFDRS) is high to extreme and the following weather parameters are forecasted to be met:
- A sustained wind average 15mph or greater
- Relative humidity less than or equal to 25%
- A temperature of greater than 75℉.
In some states, dry lightning and unstable air are criteria. A Fire Weather Watch may be issued prior to the Red Flag Warning.