This is the term used by fire-weather forecasters in the United States to call attention to weather that may affect fire behavior - for example, any combination of particularly dry conditions, extreme heat, very low humidity, or high winds. Wildland fire fighting agencies use this information to keep an eye on wildfires and, hopefully, prevent them.

How Is a Red Flag Warning Chosen?

The National Weather Service's "Fire Weather Watch / Red Flag Warning Program" uses the following criteria to issue a red flag warning:

  • Relative humidity below 35% for 4 or more hours
  • Relative humidity below 35% for any duration and wind speed greater than 15 mph
  • Forecast afternoon dispersion index greater than 75

Different regions of the United States have their own ideas about what this means and what to do about it. For example, the Florida Department of Forestry is the only state that issues their own red flag warnings, which they base on the above criteria. Florida is hot and humid, and issues these warnings frequently. By contrast, California (a state with a wide range of climates including mountain ranges, coastline, and Death Valley) waits for the National Weather Service to give the nod before issuing a warning for any area.

How Is a Red Flag Warning Given?

In many tinder-dry locations, or areas with a lot of fine flashy fuels, volunteers throughout the community post official red flags at crucial points. This way, the entire community can be aware of critical weather patterns like post-drought lightning or low humidity, and make safer decisions about potentially dangerous situations.

Some locations also feature citizen patrols, in which volunteers are trained in "fire communications" like map reading and fire reporting, and scheduled to patrol residential and high-risk areas.

Red Flag Warnings are often preceded by a Fire Weather Watch, which is issued when the National Weather Service is reasonably certain that a "Red Flag event" will occur within 72 hours. Red Flag Warnings themselves can be issued when forecasters anticipate such an event within the next 24 hours, as well as when an event is already in progress.

Does YOUR Community Have a Red Flag Program?

You know best, of course. But here are some communities which have red flag programs of their own listed online, beyond the National Weather Service's work:

  • Forest Lakes, Arizona:
  • Harney County, Oregon:
  • Colorado:
  • Kernville, California:
  • Los Angeles, California area:
    and their Greater Laguna Coast:
  • Santa Barbara County, California:
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