Fire Weather Terms

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Fire Weather Forecasts
Information and Terminology

The Grand Junction Weather Office provides a user-oriented fire weather forecasting service tailored for use by federal, state, and county land and fire management agencies as well as state and county emergency management organizations within our forecast area. The types of forecasts prepared by the Grand Junction Weather Office include general fire weather forecasts, general smoke management forecasts, fire-specific forecasts (called spot weather forecasts), fire weather watches, and red flag warnings.

The general fire weather and smoke management forecasts are issued routinely by the Grand Junction Office from April 1 through October 31 of each year. This time period is commonly considered to be western Colorado’s and eastern Utah’s "fire weather season". Fire weather watches and red flag warnings can be issued any time of the year but occur predominantly during the fire weather season. Spot weather forecasts for wildfires and prescribed burns are issued only upon request. Requests for spot weather forecasts for prescribed burns are accepted from federal and non-federal agencies.

Fire Weather Forecast Terms:

Clearing Index - An index that relates atmospheric stability and wind to the air pollution potential of an area. Lower values indicate a greater potential for air stagnation and air pollution problems.

Diurnal - Daily actions which are completed within 24 hours and which recur every 24 hours (usually in a cyclical pattern).

Downslope/Downvalley - Moving from a higher elevation to a lower elevation.

Dry Thunderstorm - A thunderstorm that produces less than 0.10 inch of precipitation.

Haines Index - An index from 2 (lowest) to 6 (greatest) that relates atmospheric stability and moisture content of the lower atmosphere to the potential for large plume-dominated fires.

LAL (Lightning Activity Level) - A rating from 1 (lowest) to 6 (greatest) related to the frequency of cloud-to-ground lightning strikes in a 2500 sq. mile area (50 mi. x 50 mi).

Mixing Height - The maximum height above the ground surface to which smoke will rise. The air is considered thoroughly mixed up to the mixing height (which acts as a cap, causing the smoke to stop rising and "flatten out").

Red Flag Criteria - A combination of "High" or "Extreme" fire danger and critical weather conditions that could cause extensive wildfire occurrences or create a critical fire control situation.

Transport Wind - The average wind direction and wind speed between the surface and the mixing height (the mixed layer).

Upslope/Upvalley - Moving from a lower elevation to a higher elevation.

Other Fire Weather Products Issued:

Red Flag Warning

A Red Flag Warning is a non-routine, special forecast alerting fire managers of critical or rapidly changing weather conditions that will increase the fire danger in a significant way. Depending on the fire danger and weather conditions, this product may be issued infrequently or several times each year.

A Red Flag Warning normally requires the combination of "High" or "Extreme" fire danger (as determined by the land management agencies) and critical weather conditions (as determined by the meteorologist). These critical weather conditions include, but are not limited to, thunderstorms producing frequent lightning but little rain (called "dry" thunderstorms), the first occurrence of lightning after a hot and dry spell, a significant increase in wind speed and/or air temperature, a significant decrease in relative humidity.

In short, a Red Flag Warning covers any combination of weather and fire danger that, together, would create a critical fire control situation or extensive wildfire occurrences!

Fire Weather Watch

This is a special product that alerts users to the possibility that red flag criteria, and therefore a red flag warning, may develop within the next 12 to 48 hours.

Smoke Management Forecast

This is a 24-hour qualitative forecast of atmospheric conditions such as wind, the existence (or not) of temperature inversions, and atmospheric stability that could affect smoke dispersal.

Spot Weather Forecast

This is a detailed forecast for a specific burn site that helps fire managers and firefighters plan for and predict fire behavior. It is issued only upon request.

National Fire Danger Rating System (NFDRS) Trends Forecast

This forecast is a trend forecast of weather parameters input into the NFDRS. The NFDRS measures wildland fire danger at observation sites throughout the Grand Junction Forecast Office area of responsibility. The weather input, combined with user input, allows the NFDRS software to predict the next days fire danger.

NWS Grand Junction Fire Weather Page (real-time data and forecasts)