The Santa Ana winds , occasionally referred to as the devil winds , [ 1 ] [ 2 ] are strong, extremely dry katabatic winds that originate inland and affect coastal Southern California and northern Baja California. They originate from cool, dry high-pressure air masses in the Great Basin. Santa Ana winds are known for the hot, dry weather that they bring in autumn often the hottest of the year , but they can also arise at other times of the year.
Typically, about 10 to 25 Santa Ana wind events occur annually. Most recently, the winds are known as the force behind the January Southern California wildfires , having gone on and off for 17 days, starting on January 6th, The Santa Anas are katabatic winds Greek for "flowing downhill" arising in higher altitudes and blowing down towards sea level.
Any low-pressure area over the Pacific Ocean, off the coast of California, can change the stability of the Great Basin High, causing a pressure gradient that turns the synoptic scale winds southward down the eastern side of the Sierra Nevada and into the Southern California region. This dry airmass sweeps across the deserts of eastern California toward the coast, and encounters the towering Transverse Ranges , which separate coastal Southern California from the deserts.
Mountain passes which channel these winds include the Soledad Pass , the Cajon Pass , and the San Gorgonio Pass , all well known for increasing Santa Anas as they are funneled through. The air has already been dried by orographic lift before reaching the Great Basin, as well as by subsidence from the upper atmosphere, so this additional warming often causes relative humidity to fall below 10 percent.
The end result is a strong, warm, and very dry wind blowing out of the bottom of mountain passes into the valleys and coastal plain. During Santa Ana conditions it is typically hotter along the coast than in the deserts, [ 14 ] with the Southern California coastal region reaching some of its highest annual temperatures in autumn rather than summer.
