Oct. 27: Firefighters from the state Department of Forestry try to control the Esperanza Fire in Banning, Calif., 90 miles east of Los Angeles.
The hot, dry Santa Ana winds are a well-known phenomenon in Southern California that can contribute to the cause and spread of wildfires in the region.
The winds sporadically blow from the eastern deserts to the Pacific during the autumn and early winter, reversing normal wind patterns in the region and warming the normally cool coastal region.
Although most believe the winds' temperature comes from the desert heat, Santa Anas actually develop when the desert is cold, peaking in December, although they can continue through March.
When high pressure builds over the Great Basin, the high, dry plain between the Sierra Nevada and Rocky Mountains that comprises eastern California, western Utah and most of Nevada, the cold air begins to sink, and is forced downward.
This process compresses and thus warms the air at the relatively rapid rate of 29 degrees Fahrenheit per mile of lost altitude.
As the temperature rises, the relative humidity falls, and the air becomes drier as it heads toward sea level.
The Santa Anas then pick up speed as they travel through the numerous mountain passes and canyons of southwestern California.
As the hot, dry, rapid winds blow through the canyons, they parch local vegetation like a giant hair dryer, priming the area for wildfires caused by any opportunistic spark.
When blazes do break out, the heat and speed of the winds only add to the flames, fanning them westward toward residential areas.
The Santa Ana winds have been studied extensively since about 1950, but have been occurring for thousands of years, probably since the giant Ice-Age era lakes of the Great Basin dried up, leaving the Great Salt Lake and Lake Tahoe, among others, as remnants.
The winds, sometimes called "devil's breath," are mentioned often in the popular culture of Southern California, most memorably in Raymond Chandler's 1938 short story "Red Wind," which describes "hot dry [winds] that come down through the mountain passes and curl your hair and make your nerves jump and your skin itch. ... Meek little wives feel the edge of the carving knife and study their husbands' necks. Anything can happen."
Resident of the region consider the hot, dry conditions associated with the winds "earthquake weather," though there is no evidence of any link to seismic activity.
"The Santa Ana Winds," Department of Atmospheric and Oceanic Studies, University of California, Los Angeles
"Santa Ana," Scripps Institute of Oceanography, Climate Research Division, University of California, San Diego