How This Fire Danger Estimate Is Calculated

This Fire Danger Estimate is a weather-based assessment developed for the Colorado Fire Training Officers Association using current National Weather Service (NWS) observations, forecasts, and active fire-weather alerts. It is designed to help firefighters, fire officers, emergency managers, and the public quickly recognize weather conditions that increase the potential for rapid fire growth.

Unlike the National Fire Danger Rating System (NFDRS), this estimate does not model live fuel moisture, dead fuel moisture, drought indices, Energy Release Component (ERC), or Burning Index (BI). Instead, it evaluates the current atmospheric conditions that most strongly influence fire behavior during the next several hours.

Weather Variables Evaluated

The estimate continuously evaluates several meteorological factors obtained directly from the National Weather Service:

Relative Humidity (RH)

Relative humidity is one of the strongest indicators of fire potential. As humidity decreases, fine fuels such as grasses, leaves, pine needles, and small twigs lose moisture rapidly and ignite more easily. Lower humidity values receive progressively higher weighting within the calculation.

Wind Speed and Wind Gusts

Wind supplies oxygen to combustion, increases the rate of spread, carries embers farther ahead of the fire, and can rapidly change fire behavior. Both sustained wind speeds and forecast gusts are evaluated because gusts frequently produce sudden increases in fire intensity and spotting potential.

Temperature

Higher temperatures contribute to fuel drying and reduce relative humidity during the daytime. Temperature is used as a secondary factor that slightly increases the fire danger estimate during unusually hot conditions.

Forecast Precipitation

Expected rainfall lowers fire potential by increasing fuel moisture. Forecast precipitation probabilities and recent measurable precipitation reduce the calculated fire danger because wet fuels require additional heat before ignition.

National Weather Service Fire Weather Alerts

When the National Weather Service issues a Fire Weather Watch or Red Flag Warning, those alerts are incorporated directly into the calculation. A Red Flag Warning automatically raises the estimate to the highest danger category because it indicates that critical fire weather conditions are expected or already occurring.

Scoring Methodology

Each weather variable contributes a weighted value based on its influence on fire behavior. Conditions such as extremely low humidity, strong winds, high temperatures, and Red Flag Warnings increase the overall score. Recent rainfall or high probabilities of precipitation reduce the score because they decrease ignition potential and fire spread.

The combined score is then classified into one of five fire danger categories:

• Low
• Moderate
• High
• Very High
• Extreme

The scoring thresholds were selected to provide a simple, transparent, weather-based estimate that reflects changing atmospheric conditions throughout the day.

Important Limitations

This tool estimates weather-related fire danger only. It does not account for many factors that fire agencies consider when establishing official fire danger ratings or burn restrictions, including:

• Fuel type and loading
• Live and dead fuel moisture
• Drought conditions
• Topography and slope
• Aspect and solar exposure
• Recent fire activity
• Available firefighting resources
• Local agency policies

Because of these additional factors, official fire danger ratings, burn bans, and fire restrictions established by local fire departments, counties, sheriffs, state agencies, or federal land-management agencies may be higher than the estimate displayed by this tool.

Users should always follow the most restrictive local fire restrictions and official guidance for the area in which they are operating.