4. Building a Mental Model of the Weather Forecast

A mental model is your representation of the world around you and a mental model of a weather forecast is your perception of how the weather will play out over time. A mental model will help you visualize the upcoming shift and will ensure that you have the best understanding of how the weather will evolve through the operational period.

Building a mental model takes several steps:

1. You must first fully understand the current forecast.
   1. Ensure you have the correct forecast for your area and operational period by reading the header information.
   2. Look for any headlines such as Advisories, Watches, or Warnings. If a headline is in the forecast, make a note of when it is valid for and what type(s) of hazards are expected.
   3. Read the discussion. The discussion should give you an idea of the larger scale weather pattern and how the forecast variables will evolve through the day. Focus will be given to any significant weather that is expected to impact safety or operations.
   4. Read through the Mandatory Elements. Compare with the discussion to see how the forecast elements may evolve with time through the operational period. Focus on frontal passages, wind shifts, and/or thunderstorm timing, if applicable.
   5. Read through the Optional Elements. These will help you understand information about stability, smoke impacts, and favored spotting direction. Also read the extended forecast to better understand the potential for high-impact weather in the coming days.
   6. Briefly discuss the forecast with your fellow firefighters. Ask yourself and others if the forecast makes sense and if you do not understand any portion of it, be sure to contact the meteorologist.
2. Look at the current weather observations. If you are on an assignment, take observations first thing in the morning. If you are on station, either go outside, and take observations, or look online at nearby weather stations as shown in Figure 1. This is important because the current weather is the starting point, and the forecast is the pathway for the weather through the shift. If the morning temperature is 70 °F and the forecast calls for a high temperature of 95 °F, you know that you will see an increase in temperature through the day. Ask yourself several questions:
   1. How will the temperature increase from now until then?
   2. Is there an inversion that may break suddenly and increase the temperature? If so, what time will it break?
   3. Is there a cold front moving through that may create a situation where the high temperature is reached early in the day?

​These questions can likely be answered by reading the forecast discussion and examining other elements within the forecast.

Figure 1: Fire weather observations from Mesowest.

3. If you are assigned to an incident or are heading to an emerging incident, your mental model needs to include knowledge of the terrain you are working in. Examine a topographic map (Figure 2) of the fire area and look at where the fire is relative to terrain features. This will help you better understand how the wind will flow through the terrain, how the different aspects will warm/cool with a changing sun angle, and how any local winds might affect your area.

Figure 2: Division personnel examining a topographic map on the Carpenter Road Fire.

4. Verify your mental model. As the day progresses, continue to either take weather observations or look at the data from nearby weather stations, like shown in Figure 3. Once again, ask yourself several questions:
   1. Is the temperature and relative humidity following the common diurnal pattern? If not, what might be causing the change?
   2. Is the wind speed and direction similar to the forecast? Is topography playing a large role in altering the speed and direction from what the forecast says?
   3. Is there cloud cover? How is it evolving? Are there thunderstorms forming? If so, can you contact dispatch or the meteorologist to find out where they are at and where they are going? Ask about the potential for gusty outflow winds.
   4. Is the forecast generally on track? If you notice that the weather is differing markedly from the forecast, you may need to contact the meteorologist and ask for an update and/or discuss your concerns.

Figure 3: A permanent RAWS.

Building a complete mental weather model is essential and going through these steps will help you better understand and follow the weather conditions as you complete your shift. Remember Standard Firefighting Order #1: Keep informed on fire weather conditions and forecasts.

The fire environment is constantly changing. Building a mental weather model and then verifying that model will help you to understand what is causing the transitions you may be observing in the fire on the ground. Recognize that the two other components of the fire environment—fuels and topography—will also play a role in the behavior of the fire. Watch for times when each of the elements of the fire behavior may align as these conditions represent the most critical times for large fire growth. Fire is dynamic, but by being a student of fire, you can better anticipate and react to the consequential changes fire behavior.