And the leaves still fall off the sweet gum trees in December. The usual airflow here is from the ocean to the desert. This explains Southern California's almost constant air-conditioned climate. But occasionally, and especially during this time of the year, a high pressure system settles in over Nevada or Utah. This sets up a flow of air contrary to the usual pattern.
Dry winds blow in from the desert, down over the mountains and out to the coast.
West of the mountains, as the air moves downhill, it heats by compression, gaining about 5.5 degrees F for every 1000 feet of descent During a strong Santa Ana the winds really pick up, reaching gale-force proportions. Southern California often tops the Country's temperature charts on these days. The tourists are gone, the weather's still great, and the locals are back to work. About earthquakes, your chances of being injured in a quake are just about up there with being struck by lightning. In 1996, Southern California experienced 18,051 earthquakes.