National Wildfire Coordinating Group

Extreme Fire Behavior – I


3. Base all actions on current and expected behavior of the fire. A firefighter looks at his watch, which reads 2 PM, while a fire actively grows in steep terrain and heavy timber.

3. Base all actions on current and expected behavior of the fire.

Fire managers make decisions throughout the day on how to suppress fires and best use resources while protecting life and property. This Standard Firefighting Order depicts a firefighter observing increased fire behavior during a time of day when temperatures are high and relative humidity is low.

Read about all 10 Standard Firefighting Orders.

Changes in fire behavior have always been present in cases of shelter deployment. It is critical for firefighters to maintain situation awareness of live and dead fuel moisture conditions, as well as predicted and current weather conditions. As fire behavior moves from mild to moderate to extreme, it is critical to act decisively regarding the changing situation.

Discuss the following indicators of extreme fire behavior:

  • Relative humidity less than 15%.
  • 1-hour fuel moisture less than 5%.
  • Transition from surface to crown fire.
  • Smoldering fires that exist in the early part of the day are beginning to burn very actively as the day progresses.
  • Approaching thunderheads with dark clouds beneath.
  • Presence of dust devils indicating atmospheric instability.
  • Increased spotting.
  • Sudden calm.
  • High clouds moving fast in a direction that is different from surface wind.
  • Predicted Haines Index of 5 and 6 in those areas where this level is a good indicator of atmospheric instability.
  • Fire whirls.

Image of a fire whirl twisting up from a forest fire.


Weather - Fire Behavior
Page Last Modified / Reviewed: 
Feb 2021

Have an idea or feedback?
Share it with the NWCG 6MFS Subcommittee.

Follow NWCG on Twitter  and Facebook