What Is a Red Flag Warning?


A red flag warning is issued by the National Weather Service to alert people of dangerous weather conditions that have a high probability of resulting in fires. The issuing of a red flag warning requires specific criteria.


  • Three criteria are considered prior to issuing a red flag warning. These measurable readings include sustained wind speeds, relative humidity, and 10-hour fuel moisture.

Local Conditions

  • The specific conditions for red flag warnings are established by local offices of the National Weather Service. For example, the Chicago NWS lists them as sustained winds at 20 feet of 20 mph or greater, relative humidity of 25 percent or less when measured in the afternoon, and a reading of 8 percent or less for one day's 10-hour fuel moisture.


  • Red flag warnings are an important part of the weather notification system that keeps people and property safe. They are issued when the dangerous conditions are projected to occur within 24 hours.


  • When a red flag warning is issued by the NWS, you should make preparations according to the directions provided with the warning. This normally includes common fire safety precautions, as well as additional directives given by local or city governments regarding restricted activities.

Red Flag Warnings Online

  • The National Oceanic and Atmospheric Administration's National Weather Service website provides comprehensive information regarding red flag warnings throughout the United States. The website is easy to use and is constantly updated with the most current weather watches and warnings.

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  • Photo Credit Image by Flickr.com, courtesy of traveling for about a month) (Jeremy Barwick
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