Southern California is prone to wildfires. But looking at the previous year data, the event during this time of December is uncommon.
The major reason of these rapidly spreading wildfires could be attributed to the dry conditions across the region along with Santa Ana winds. These winds are a commonly prevail in Southern California between October and March. The heat embedded in these wind wrecks destruction throughout the region, for instance knocking down trees and power lines, dries out vegetation, making it easier to burn.