What Is A Red Flag Warning?

Wildfire Fighting Forecasting Extreme Burning Conditions

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Updated on March 06, 2017

The United States National Weather Service is one major forecaster that determines a "Red Flag Warning" when weather conditions reach high potential for extreme wildfire starts leading to uncontrolled forest fires. It is a term used by fire-weather forecasters to call attention to critical weather conditions of particular importance that will potentially result in extreme burning conditions. It is must have continuously updated data for field foresters, wildland fire crews and equipment operators during periods of high fire hazard.

A Red Flag Warning or RFW can be issued either by the state or the federal government to assist regional firefighting and land management agencies in making decisions on limiting the use of fire for a particular period of days or fighting fire when conditions suggest increased chances. Conditions that increase the chance of wildland fire starts and fire spread are monitored and a RFW is issued when a high degree of confidence that Red Flag conditions will occur within 24 hours of issuance.

So, a RFW is usually issued from predictions based on drought conditions and when the relative humidity is very low. High winds and dry lightning strikes can become exacerbating factors and are included in some state and federal agencies that calculate their own warning data. These agencies will alter their staffing and equipment resources according to the data. To the public, a Red Flag Warning means high fire danger with increased probability of a quickly spreading vegetation fire in the area within 24 hours. Extreme care should be taken and the uses of outside fire suspended.

Red Flag criteria also occur whenever a region (usually a state) has been in a dry spell for a week or two, or for a shorter period under duress. It usually happens either before spring green-up or after fall color in the East or during the hot, windy summer in the West. The National Fire Danger Rating System (NFDRS) is usually high to extreme and the following forecast weather parameters are forecasted to be met:

Sustained wind averages of 15 mph or greater.
Relative humidity less than or equal to 25 percent.
A temperature of greater than 75 degrees F.
In some states, dry lightning and unstable air are criteria.

A Fire Weather Watch may be issued prior to the Red Flag Warning.