Wildfires in Southern California have been raging throughout most of January. Fighting these fires requires not only skill and experience but also a strategic understanding of environmental conditions to help limit their spread. What makes wildfires spread? Drought Warm weather Low humidity Strong winds Topography What is the best time of day to fight wildfires? The best time of day to fight wildfires, according to experienced brush fire firefighter James Burwell, is overnight through the early morning hours, just before sunrise. Why? COOL TEMPERATURES: The lowest temperatures of the day occur just before sunrise when the sun’s angle is very low. During this time, the radiation emitted from the surface at night outweighs the weak solar radiation from the rising sun. HIGH HUMIDITY: This humidity isn’t extremely high like the kind seen in Florida, but rather enough moisture in the air to help weaken fires. For higher humidity, the temperature and dew point need to be close to one another, aiming for 100% relative humidity or complete saturation. At night and into the morning, the temperature doesn’t need to drop as quickly (compared to the day) to reach the dew point resulting in higher humidity. WEAK WINDS: Surface heating drives wind development, but at night, the atmosphere stabilizes due to the lack of heating, leading to calmer conditions. While factors like drought and topography are immutable and play a significant role in the growth and spread of fires, some firefighters use tactics like starting “backfires” in rapidly spreading regions. This technique occurs ahead of established fires and helps deprive the fire of fuel, preventing it from reaching areas with unpredictable behavior.