National Weather Service
The National Weather Service has alerts for weather conditions that are ripe for a fire:
Criteria: A combination of weather and fuels conditions (as determined by fire management) for any 3 hours or more in a 12 hour period.
1. Frequent gusts of 25 mph or greater – AND relative humidity of 15% or less
2. Dry thunderstorms (15% coverage or more, constituting an LAL 6.)
OTHER FACTORS:
In addition to the basic criteria above, a combination of other elements may result in Red Flag Conditions:
3. Haines Index of 5 or 6, indicating a moderate or high potential for large, plume dominated fire growth.
4. Wind shifts associated with frontal passages.
5. First significant lightning event (wet or dry) after an extended hot and dry period.
6. Poor relative humidity recovery overnight (RH remains at 40% or lower.)
7. Any combination of weather and fuel moisture conditions which, in the judgment of the forecaster, would cause extensive wildfire occurrences.
Fire Weather Warning:
A Fire Weather Watch is issued up to 72h before the above conditions are expected to occur. This is an alert to land management agencies to the high potential for development of Red Flag Criteria in the next 12-72hours.
Red Flag Warning:
Red Flag Warning: Issued when the conditions above are expected to occur or are occurring within the next 24h. It is based on a combination of weather and fuels conditions (determined by fire management) for any 3hours or more in a 24hour period.