What does a red flag warning mean?

Blog Post created by tomwelle on May 29, 2015

As we move into the “Act” phase of the Year of Living Less Dangerously From Wildfire, the safety of Image1residents and firefighters is foremost on our minds here at NFPA.  One of the products that the National Weather Service, (NWS) provides to improve firefighter safety is the Red Flag Warning.  But just what is a Red Flag Warning?

Red Flag Warnings begin as a Fire Weather Watch.  A Fire Weather Watch means that weather conditions are predicted to occur that will support rapid wildfire growth and rates of spread 24-72 hours from when the watch is issued.  When the conditions are predicted to occur within 24 hours or are already happening, a Red Flag Warning is issued.

So, what are these conditions?  Well, that depends.  In the broad sense, the weather conditions will be high temperatures, high surface winds, low relative humidity, (dry air) and low fuel moistures, (dry vegetation).  However, these vary state to state.

Each year, the National Weather Service coordinates with each state to implement a State Operating Plan related to fire weather services.  According to NWS Fire Meteorologist Chris Cuoco, these meetings take place at the Geographic Area Coordination Centers where the state and federal agencies such as the U.S. Forest Service and Department of Interior are represented. Red Flag criteria and other fire weather products are discussed and set in these meetings.  The Red Flag Warning criteria varies state to state mainly around relative humidity and fuel moistures.   In the humid Southeastern U.S., relative humidity of less than 30% can trigger a Red Flag, but is no big deal in the arid West where critical relative humidity is often in the single digits.  The same goes for fuel moisture values.  And it is usually not any one condition but the combination of these Srh conditions cause Red Flags to be issued.

While the primary purpose of Red Flag Warnings is firefighter safety, fire agencies and land management agencies  also use them for pre-planning, staffing level changes, and if necessary, restrict some public activities such as camp fires and agricultural burns.

The NWS has been active in making the public more aware of these Watches and Warnings.  Cuoco said, “The hope is that when the public is using fire, they will use the caution implied in those products.” 

 photo credit: top, bottom  srh