There are three components needed to start a wildfire: fuel, oxygen/air, and heat. These three elements are considered the “fire triangle.” Firefighters know that if any one of the components is removed, a wildfire will not occur or can be suppressed.
Weather is usually the largest variable affecting this fire triangle, and it is important for wildland firefighters to know and understand the current and expected weather conditions during both the short and long term.
The main weather components wildland firefighters use to predict the potential for wildfire are:
Wind usually has the strongest effect on fire behavior, and typically the most extreme wildfire events are directly related to high wind speeds. In addition to its ability to “fan the flames,” wind is often the most variable weather factor throughout the day, and can change both a wildfire’s direction and intensity in an instant. Abrupt changes in wind speed and direction are typically the result of an unstable atmosphere. This condition is typically a wildland firefighter’s greatest challenge in suppressing a wildfire.
Temperature has a direct influence on fire behavior, because heat drives the ignition and combustion process. Temperature also affects relative humidity, which affects a fire’s intensity. Fortunately, temperature is easy to predict, and its daily changes follow a similar pattern from one day to the next.
Relatively humidity is the amount of moisture present in the air. This moisture influences the potential of forest fuels to ignite and burn, as well as influencing the amount of heat that fuels give off during the combustion process. Relative humidity fluctuates widely throughout the course of the day; it is usually highest in the early predawn hours and lowest during the afternoon.
Precipitation directly affects both fuel moisture and relative humidity. Rainfall patterns greatly affect the overall fire season as well as the daily potential for wildfires.
Here are some excellent website links to wildland fire-related weather information:
Fire Weather Information Links
- National Weather Service – Fire Weather – national fire weather forecasting site
Several National Weather Service (NWS) forecast offices share in the complete coverage of weather forecasting for Virginia. These forecasts are used daily by fire managers. https://www.weather.gov
How Weather Impacts Wildfire
The following website link provides a more thorough discussion on weather’s influence and the role weather plays for fire managers.
- How to Predict Forest Fire Behavior – Understanding Forest Fire Weather to Fight Wildfire
The following website link provides national level information on the Palmer Drought Index. This index uses seasonal precipitation as an excellent longer-term predictor of the potential for wildfire.
- Palmer Drought Index – Drought severity index, updated weekly
Read today’s daily fire danger rating and Wildfire Summation Report.