What is a Red Flag Warning and what can you do when one is issued?

Blog Post created by luciandeaton Employee on Jun 19, 2020

Wildfire Red Flag Warning

With recent dry weather bringing Red Flag Warnings to communities across the Southwest and Western United States, it’s important to understand what triggers a “Red Flag Warning, what those conditions mean, and what you can do when one is announced in your area to make your home and community safer from wildfire. 

You will see in weather reports on the news that Red Flag Warnings begin as a Fire Weather Watch.  A Fire Weather Watch means that weather conditions are predicted to occur that can support rapid wildfire growth and rates of spread 24-72 hours from when the watch is issued. 

When those conditions are predicted to occur within 24 hours, or are already happening, a Red Flag Warning is then issued.  

So, what are the conditions that combine to create such risk?  In the broad sense, they are:

  • High temperatures,
  • High surface winds,
  • Low relative humidity, and
  • Persistence of dry air and low fuel moisture that creates dry vegetation. 


Red Flag Warning criteria varies state to state, mainly concerning relative humidity and fuel moisture.   For example, relative humidity of less than 30% in the humid Southeastern U.S. can trigger a Red Flag Warning, while this would not be a threshold in the arid Western U.S. where critical relative humidity is often in the single digits.  The same goes for fuel moisture values. 


It’s important to remember that the combination of conditions cause Red Flag Warnings to be issued and they are locally specific.  Your local fire authority will have more information on how these are issued and guidance for local action on what activities are restricted during such periods. 

When a Red Flag Warning is announced, there are steps you can take.  Check out this brief video sharing 2 steps for immediate action to make your home and community safer from wildfire.

Photo Credit: NIFC Photo Library

As we navigate the evolving situation with COVID-19, NFPA remains committed to supporting you with the resources you need to minimize risk and help prevent loss, injuries, and death from fire, electrical, and other hazards. For information on NFPA’s response to the coronavirus, please visit our webpage.

Follow NFPA’s FireBreak blog and you can also follow me on twitter @LucianNFPA for more international wildfire and policy related topics.