<P> Santa Ana winds are known for the hot dry weather that they bring in the fall (often the hottest of the year), but they can arise at other times of the year . They often bring the lowest relative humidities of the year to coastal Southern California . These low humidities, combined with the warm, compressionally - heated airmass, plus high wind speeds, create critical fire weather conditions . Known as "devil winds", Santa Anas are infamous for fanning regional wildfires . </P> <P> The National Weather Service defines Santa Ana winds as "Strong down slope winds that blow through the mountain passes in southern California . These winds, which can easily exceed 40 miles per hour (18 m / s), are warm and dry and can severely exacerbate brush or forest fires, especially under drought conditions ." </P> <P> The Santa Anas are katabatic winds--Greek for "flowing downhill", arising in higher altitudes and blowing down towards sea level . Santa Ana winds originate from high - pressure airmasses over the Great Basin and upper Mojave Desert . 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 . Cool, dry air flows outward in a clockwise spiral from the high pressure center . This cool, 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 . The airmass, flowing from high pressure in the Great Basin to a low pressure center off the coast, takes the path of least resistance by channeling through the mountain passes to the lower coastal elevations, as the low pressure area off the coast pulls the airmass offshore . </P> <P> These passes include the Soledad Pass, the Cajon Pass, and the San Gorgonio Pass, all well known for exaggerating Santa Anas as they are funneled through . As the wind narrows and is compressed into the passes its velocity increases dramatically, often to near - gale force or above . At the same time, as the air descends from higher elevation to lower, it is heated adiabatically, warming about 5 ° F for each 1,000 feet it descends (10 ° C for each 1,000 m). As it warms, its capacity to hold moisture increases, so its relative humidity decreases . 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 . </P>

Where do the santa ana winds come from
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