Wildfires regularly burn large areas of chaparral and adjacent woodlands in autumn and winter in southern California. These fires often occur in conjunction with Santa Ana weather events, which combine high winds and low humidity, and tend to follow a wet winter rainy season. Because conditions fostering large fall and winter wildfires in California are the result of large-scale patterns in atmospheric circulation, the same conditions are likely to occur over a wide area at the same time. Furthermore, over a century of watershed reserve management and fire suppression have promoted fuel accumulations, helping to shape one of a conflagration-prone environment. Combined with a complex topography and a large human population, southern Californian ecology and climate pose a considerable physical and societal challenge to fire management.

This study analyzes fire histories from four national forests in coastal southern California to identify antecedent climatological and concurrent meteorological conditions conducive to the ignition and rapid spread of large wildfires in multiple locations across the region. There are distinct patterns in both antecendent moisture and atmospheric circulation associated with the occurrence of large fires in autumn and winter in coastal southern California.