What is a 'Red Flag Warning'? Weather Caution Meaning Explained

A red flag warning comes around fairly rarely and is something people should be aware of. The West Coast has been hit by red flag warnings in the past, meaning citizens should prepare for some extreme weather coming their way.

The warning actually comes from fire-weather forecasters as well as the National Weather Service, and is linked to the National Fire Danger Rating System.

We break down what this weather warning means and what could happen.

What Is a Red Flag Weather Warning and When Are They Issued?

A red flag weather warning is used by fire-weather forecasters when the weather could lead to burning conditions, such as wildfires.

It's used when there are concerns the criteria for a red flag warning could occur within the next 24 hours, giving people some time to prepare.

Usually, the conditions are created when an area has had a dry spell that could increase the risk of fire. This is made clear by the National Fire Danger Rating System, which must be at high to extreme in order to issue a red flag warning.

Heath Hockenberry, the National Fire Weather Program Manager for the National Weather Service, told Newsweek: "Red Flag Warnings are 'fire environment' products that combine weather conditions and also fuel conditions. The fuel conditions include how dry the vegetation is and how effectively the fuels can burn.

"So when a Red Flag Warning is issued, it means that these combined conditions are favorable for fast-moving and uncontrollable fires. Red Flag Warnings do not attempt to predict where a fire is, where it will start, or exactly where it will move."

He also said the way in which fires can start from these conditions are not very predictable, meaning there is no telling where a fire could ignite after this warning is issued.

Examples of Red Flag Weather Conditions

In short, a red flag warning means there is an increased risk of fire danger due to the combination of warm temperatures, very low humidity and stronger winds.

More specifically, the National Weather Service criteria for a red flag warning are as follows:

  • A sustained wind of 15 mph or greater on average
  • A temperature higher than 75 degrees Fahrenheit
  • Relative humidity of 25 percent or lower

Some states also specify unstable air or dry lightning are criteria for a red flag warning.

They could issue a fire weather watch first, before moving to a red flag warning if conditions were to worsen.

In recent years, the West Coast has received many red flag alerts ahead of wildfires, with the California Fire Department issuing warnings to civilians to take extreme care.

Guidance for Red Flag Warnings

The National Weather Service calls on civilians to be cautious around fire, with particular suggestions in place to stop the potential for a wildfire.

Hockenberry explained how the public should avoid open burning, such as campfires or fireworks, and that these warnings serve to "heighten awareness" of potential fire.

He said: "A Red Flag Warning means that any fire that starts will likely spread quickly. It should be an indicator that evacuations may be possible and everyone should stay in touch with local authorities for any notices or actions necessary to leave the area if needed."

Other actions he mentioned included clearing dry fuels from around your home and making it less susceptible to fire to prevent any blaze beginning.

In the California Fire Department guidelines, they add other suggestions such as avoiding throwing matches or cigarettes from moving cars, and properly extinguishing any open fires or live coals with water.

Tips on preparing your property can be found through the Ready, Set, Go program at the National Weather Service.

wildfires in california
A jet dropping a fire retardant over the Sherpa Fire in California in 2016. 'Newsweek' explains the meaning of a red flag warning. David McNew/Getty Images