Name the four primary weather factors that affect wildland fires.

• A. Atmospheric pressure, humidity only, cloud cover, and rainfall frequency.
• B. Wind and temperature only.
• C. Soil moisture, precipitation, wind, and altimeter setting.
• D. Temperature, relative humidity, wind, and precipitation/drying tendencies.

Answer: (D)

Weather drives how a wildfire ignites, grows, and moves. The four primary factors are temperature, relative humidity, wind, and precipitation or the drying tendency of fuels. Temperature influences how quickly fuels heat up and shed moisture; higher temperatures tend to dry fuels and speed spread. Relative humidity shows how much water vapor is in the air; lower humidity dries fuels and makes ignition and burning easier, while higher humidity helps keep fuels wetter. Wind supplies oxygen and fans flames, increasing both the rate of spread and the direction the fire travels. Precipitation cools fuels and adds moisture, reducing fire activity, while the drying tendency describes how fuels lose moisture after rain, which can quickly raise fire danger if there’s a long dry spell after rain. The other options omit or replace essential elements—for example, one set leaves out wind, another focuses on soil moisture and altitude instead of fuel moisture and drying behavior, and another emphasizes humidity alone without the full moisture and drying picture—so they don’t capture the full weather-driven controls on wildland fire behavior.