This is the time of year when the National Weather Service (NWS) regularly issues Red Flag Warnings. But just what are they?
Red Flag Warnings often begin as a Fire Weather Watch, which means that weather conditions are predicted to occur that will support rapid wildfire growth and rates of spread 24 to 72 hours from when the watch is issued. When the conditions are predicted to occur within approximately 24 hours, or are already happening, a Red Flag Warning is issued.
The conditions that trigger Red Flag Warnings include predicted weather conditions of high temperatures, sustained high surface winds, and low relative humidity (dry air), plus predicted and observed low fuel moistures (dry vegetation – live and dead), and anticipated lightning activity. It is usually not any one condition, but the combination of these factors, that cause Red Flag Warnings 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, restricting some public activities such as campfires and agricultural and forestry prescribed burns.
So, how are Red Flag Warnings communicated to the public?
- Included as part of local radio and television weather broadcasts.
- Broadcast on the Weather Alert radio network.
- Via the internet on NWS and other weather pages.
For more information, you can go to your local NWS office’s website or read this helpful and short summary: https://www.weather.gov/media/lmk/pdf/what_is_a_red_flag_warning.pdf.
Some Western U.S. locations display red flags near public buildings. The graphic at the top is one and examples of other Red Flag Warning flags are below: