Fire Weather

Fire weather is defined as those weather parameters that influence fire occurrence and subsequent fire behaviour. (e.g., temperature, relative humidity, wind speed and direction, precipitation, atmospheric stability, and winds at upper levels in the atmosphere.)

The weather is the controlling factor in determining how much of the forest fuel is available for combustion. When the forest receives significant amounts of rain no fuel is available for combustion because it is too wet. However, after several dry, hot, windy days, tons of fuel can become available for combustion. The weather has a significant impact on how hot a fire will burn and how fast it will spread.

Natural Resources operates 28 weather stations. We also monitor reports from 22 stations operated by other agencies

Every day at 1:00 p.m. during the forest fire season, DNR staff record the temperature, relative humidity, wind speed and direction and the amount of rain in the last 24 hours at each of these stations. This information is input into the Canadian Forest Fire Weather Index (FWI) System and is used by fire managers to determine if they can expect to have a fire start that afternoon and if so, what type of fire it will be. This helps them decide how many and what types of resources may be required for an initial attack on any new fires.

Presuppression Planning

By using forecasted weather and FWI for the next day, the fire manager can use the information to assist in making decisions about the following presuppression activities:

• to allow category 1 burning;
• to cancel burning permits;
• to schedule aerial detection flights and if so, how many;
• to restrict the hours that forest industry can work in the forests;
• to preposition firefighting resources in anticipation of a fire;
• to request special patrols in high hazard areas; and
• to increase prevention activities.

Suppression Activities

A Fire Behaviour Specialist will also input the weather data into the Canadian Forest Fire Behaviour Prediction (FBP) System and will be able to predict how a fire will behave in a given fuel under those weather conditions. The use of a portable weather station at the site of the fire will assist the specialist in their prediction by providing real time data at the scene of the fire. The specialist’s prediction will include information on:

• how fast the fire will spread
• where the fire will spread
• how intense the fire will burn
• what percentage of the fuel will be burned; and
• what type of fire the firefighters can expect to encounter.

This is important information for the Incident Commander and his staff to use in planning how best to attack the fire and for the safety of the firefighters.