Fire Danger Rating Signs "What Do They Mean?"
Fire Danger Rating SignsFire Danger Rating Sign Info Flyer.pdf
The purpose of the Fire Danger Rating Sign is to prevent wildfires by increasing awareness of wildfire ignition and spread potential. Wildfire ignition potential is determined by the following factors:
1) size and shape of fuels
2) compactness or arrangement of fuels
3) fuel moisture content, and
4) fuel temperature.
In general, these factors vary over a geographic area, change each day, and are not practical to continually assess. Therefore, the signs will display the Fire Danger Rating using air temperature.
Wind is the most influential factor affecting wildfire spread.
Any reliable weather forecast can be utilized and when in doubt, round up to the next higher rating.
Windy periods with low fuel moisture and relative humidity usually result in Red Flag Warnings.
Red flags will only be displayed when the National Weather Service declares a “Red Flag Warning” for any portion of Sonoma County.
The rating will be “Extreme” when red flags are posted regardless of other weather conditions.
Signs will change to “low” when there is sustained rain (over 4 hours).
May 1 – September 31: Highest predicted air temperature
October 1 – November 31: Highest predicted air temperature
December 1 – April 30
December 1st through April 30th the sign is kept at low unless weather associated with increased wildfire ignition and fuel conditions support changing. This will be a discretionary decision by the fire agencies and will be considered during significant dry periods during the winter months where prescribed burning increases the wildfire ignition potential.