The Clayton Fire that burned hundreds of structures in and near Lower Lake, California 31 air miles northeast of Santa Rosa, was rather benign Sunday morning, and some thought firefighters had a handle on it. But later in the day the wind increased and pushed it into the community, spreading much more quickly than firefighters expected or could keep up with.
We checked the weather conditions recorded at the Konocti weather station west of Lower Lake and found that the wind direction shifted by about 180 degrees at mid-day. Before noon there was a north to northeast wind at 0 to 6 mph blowing the fire away from Lower Lake. That changed very suddenly at around noon when the wind became out of the southwest and west at 12 to 14 mph with gusts of 19 to 24 mph. This pushed the fire into the community. The firefighters and other resources that were on hand were not able to keep up with the fire or protect every structure in the town.
At about the same time, the temperature went up to over 90 degrees and the relative humidity dropped from about 30 percent to around 18 percent, and may have briefly hit 8 percent.
Of all of the weather features that affect the behavior of a wildfire, a strong wind can override them all to a degree and control the direction of spread. Topography and fuels (vegetation) also help determine how a fire will spread, but if conditions are dry, wind is the ingredient that firefighters most respect.
Land managers and homeowners can control one of the three factors that determine fire behavior — fuel. It can be removed within 100 feet of structures. Large scale fuel reduction projects in the areas near communities can affect the intensity of a fire when it approaches structures, giving firefighters a chance to save them. But the other two factors, topography and weather, are out of their hands.
The weather forecast for the area of the Clayton Fire predicts clear skies for Monday, a high of 97 degrees, 14 percent relative humidity, and southeast to east winds of 5 to 10 mph. Tuesday will be about the same but with very variable winds blowing from virtually all directions during the day.