Local and synoptic mechanisms causing Southern California’s Santa Ana winds

The cool, moist fall and winter climate in Southern Cali- fornia is often disrupted by dry, hot days with strong winds blowing out of the desert. These ‘‘Santa Ana’’ winds are a dominant feature of the fall and wintertime climate of Southern California (Conil and Hall 2006), and have important human and ecological impacts. First, and most pronounced, is their effect on wildfires: following the hot, dry summer, the extremely low relative humidities and gusty strong winds that occur during Santa Anas introduce extreme fire risk which often culminates in wildfires with large economic loss.