The Santa Ana winds are strong, extremely dry down-slope 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 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.
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."
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.
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.
During Santa Ana conditions it is typically hotter along the coast than in the deserts, with the Southern California coastal region reaching some of its highest annual temperatures in autumn rather than summer.
While the Santa Anas are katabatic, they are not Föhn winds. These result from precipitation on the windward side of a mountain range which releases latent heat into the atmosphere which is then warmer on the leeward side (e.g., the Chinook or the original Föhn).
If the Santa Anas are strong, the usual day-time sea breeze may not arise, or develop weak later in the day because the strong offshore desert winds oppose the on-shore sea breeze. At night, the Santa Ana Winds merge with the land breeze blowing from land to sea and strengthen because the inland desert cools more than the ocean due to differences in the heat capacity and because there is no competing sea breeze.
Santa Ana winds often bring the lowest relative humidities of the year to coastal Southern California. These low humidities, combined with the warm, compressionally-heated airmass, plus the high wind speeds, create critical fire weather conditions. The combination of wind, heat, and dryness accompanying the Santa Ana winds turns the chaparral into explosive fuel feeding the infamous wildfires for which the region is known. Wildfires fanned by Santa Ana winds burned 721,791 acres (2,920.98 km2) in two weeks during October 2003. and another 500,000 acres (2,000 km2) in the October 2007 California wildfires.
Although the winds often have a destructive nature, they have some benefits as well. They cause cold water to rise from below the surface layer of the ocean, bringing with it many nutrients that ultimately benefit local fisheries. As the winds blow over the ocean, sea surface temperatures drop about 4°C (7°F), indicating the upwelling. Chlorophyll concentrations in the surface water go from negligible, in the absence of winds, to very active at more than 1.5 milligrams per cubic meter in the presence of the winds.
During the Santa Ana winds, large ocean waves can develop. These waves come from a northeasterly direction; toward the normally sheltered side of Catalina Island. Protected harbors such as Avalon and Two Harbors are normally sheltered and the waters within the harbors are very calm. In strong Santa Ana conditions, these harbors develop high surf and strong winds that can tear boats from their moorings and crash them onto the shore. During a Santa Ana, it is advised that boaters moor on the back side of the island to avoid the dangerous conditions of the front side.
A Santa Ana fog is a derivative phenomenon in which a ground fog settles in coastal Southern California at the end of a Santa Ana wind episode. When Santa Ana conditions prevail, with winds in the lower two to three kilometers (1.25-1.8 miles) of the atmosphere from the north through east, the air over the coastal basin is extremely dry, and this dry air extends out over offshore waters of the Pacific Ocean. When the Santa Ana winds cease, the cool and moist marine layer may re-form rapidly over the ocean if conditions are right. The air in the marine layer becomes very moist and very low clouds or fog occurs. If wind gradients turn on-shore with enough strength, this sea fog is blown onto the coastal areas. This marks a sudden and surprising transition from the hot, dry Santa Ana conditions to cool, moist, and gray marine weather, as the Santa Ana fog can blow onshore and envelop cities in as quickly as fifteen minutes. However, a true Santa Ana fog is rare, because it requires conditions conducive to rapid re-forming of the marine layer, plus a rapid and strong reversal in wind gradients from off-shore to on-shore winds. More often, the high pressure system over the Great Basin, which caused the Santa Ana conditions in the first place, is slow to weaken or move east across the United States. In this more usual case, the Santa Ana winds cease, but warm, dry conditions under a stationary air mass continue for days or even weeks after the Santa Ana wind event ends.
A related phenomenon occurs when the Santa Ana condition is present but weak, allowing hot dry air to accumulate in the inland valleys that may not push all the way to sea level. Under these conditions auto commuters can drive from the San Fernando Valley where conditions are sunny and warm, over the low Santa Monica Mountains, to plunge into the cool cloudy air, low clouds, and fog characteristic of the marine air mass. This and the "Santa Ana fog" above constitute examples of an air inversion.
The similar winds in the Santa Barbara area occur most frequently in the late spring to early summer, and are strongest at sunset, or "sundown"; hence their name: sundowner. Because high pressure areas usually migrate east, changing the pressure gradient in southern California to the northeast, it is common for "sundowner" wind events to precede Santa Ana events by a day or two.
Winds blowing off the elevated glaciated plateaus of Greenland and Antarctica experience the most extreme form of katabatic wind, of which the Santa Ana is a type, for the most part. The winds start at a high elevation and flow outward and downslope, attaining hurricane gusts in valleys, along the shore, and even out to sea. Like the Santa Ana, these winds also heat up by compression and lose humidity, but because they start out so extraordinarily cold and dry and blow over snow and ice all the way to the sea, the perceived similarity is negligible.
The Santa Ana winds and the accompanying raging wildfires have been a part of the ecosystem of the Los Angeles Basin for over 5,000 years, dating back to the earliest habitation of the region by the Tongva and Tataviam peoples.
The Santa Ana winds have been recognized and reported in English-language records as a weather phenomenon in Southern California since at least the mid-nineteenth century. Various episodes of hot, dry winds have been described over this history as dust storms, hurricane-force winds, and violent north-easters, damaging houses and destroying fruit orchards. Newspaper archives have many photographs of regional damage dating back to the beginnings of news reporting in Los Angeles. When the Los Angeles Basin was primarily an agricultural region, the winds were feared particularly by farmers for their potential to destroy crops.
The winds are also associated with some of the area's largest and deadliest wildfires, including the state's largest fire on record, the Cedar Fire, as well as the Laguna Fire, Old Fire, Esperanza Fire, Santiago Canyon Fire of 1889 and the Witch Creek Fire.
In October 2007, the winds fueled major wild fires and house burnings in Escondido, Malibu, Rainbow, San Marcos, Carlsbad, Rancho Bernardo, Poway, Ramona, and in the major cities of San Bernardino, San Diego and Los Angeles. The Santa Ana winds were also a factor in the November 2008 California wildfires.
In early December 2011, the Santa Ana winds were the strongest yet recorded. An atmospheric set-up occurred that allowed the towns of Pasadena and Altadena in the San Gabriel Valley to get whipped by sustained winds at 97 mph (156 km/h), and gusts up to 167 mph (269 km/h). The winds toppled thousands of trees, knocking out power for over a week. Schools were closed, and a "state of emergency" was declared. The winds grounded planes at LAX, destroyed homes, and were even strong enough to snap a concrete stop light from its foundation. The winds also ripped through Mammoth Mountain and parts of Utah. Mammoth Mountain experienced a near-record wind gust of 175 mph (282 km/h), on December 1, 2011.
In December 2017 a complex of twenty-five Southern California wildfires were exacerbated by long-lasting and strong Santa Ana winds.
Especially hot, dry, and dusty Santa Ana winds are widely believed (in Southern California, at least) to affect people's moods and behavior negatively. This has not been proven in studies, though limited evidence may point to this conclusion. Despite the lack of definitive evidence, it is a part of local lore.
The winds carry Coccidioides immitis and Coccidioides posadasii spores into nonendemic areas, a pathogenic fungus that causes Coccidioidomycosis ("Valley Fever"). Symptomatic infection (40 percent of cases) usually presents as an influenza-like illness with fever, cough, headaches, rash, and myalgia (muscle pain). Serious complications include severe pneumonia, lung nodules, and disseminated disease, where the fungus spreads throughout the body. The disseminated form of Coccidioidomycosis can devastate the body, causing skin ulcers, abscesses, bone lesions, severe joint pain, heart inflammation, urinary tract problems, meningitis, and often death.
The most well-accepted explanation for the name Santa Ana winds is that it is derived from the Santa Ana Canyon in Orange County, one of the many locations the winds blow intensely. Newspaper references to the name Santa Ana winds date as far back as 1886. By 1893, controversy had broken out over whether this name was a corruption of the Spanish term Santana (a running together of the words Santa Ana), or the different term Satanás, meaning Satan. However, newspaper mention of the term "Satanás" in reference to the winds did not begin appearing until more than 60 years later. A possible explanation is that the spoken Spanish language merges two identical vowels in elision, when one ends a word and the other begins the next word. Thus the Spanish pronunciation of the phrase "Santa Ana" sounds like "Santana."
Another attempt at explanation of the name claims that it derives from a Native American term for "devil wind" that was altered by the Spanish into the form "Satanás" (meaning Satan), and then later corrupted into "Santa Ana." However, an authority on Native American language claims this term "Santana" never existed in that tongue.
A third explanation places the origin of the term Santa Ana winds with an Associated Press correspondent stationed in Santa Ana in 1902, who documented the name "Santa Ana winds," or possibly mistook the term "Santana" or "Satanás" for "Santa Ana." 
Another derivation favored by the late well-known KABC television meteorologist, Dr. George Fischbeck, cited the etymology of the Santana winds as coming from the early Mexicano/Angeleno: "Caliente aliento de Satanás" or "hot breath of Satan." This is likely a false etymology or folk etymology, though.
The original term and translation for the destructive dry, strong, winds from the east in southern California, southwestern central California, and northwest Mexico, is the Spanish/Mexican “Vientos Santana”, translated into English originally as “Santana Winds,” “Satan’s Winds,” “Devil Winds” but not “Santa Ana Winds.” These Santana Winds caused fires, death, dehydration, ships to go off course, destruction of agriculature, farming, livestock, homes, villages, towns, cities, medical problems long before California became a State. Because the destruction was so severe, it was suggested by locals of prior centuries, the winds could be only from “Santana,” English translation “The Devil,” “Satan.” It is suspected the term “Vientos Santana” “Santana Winds” originated in part from the language of the local Native Indians who would have also experienced the same destruction from these winds.
The term “Santa Ana Winds” is a new age term, a modern Californized, Americanized, Anglo version of what was originally and histocially called the “Santana Winds” in California resulting from the slower, less romantic language or less Latin based pronunciation, and a more enunciated and deliberate form of speech increasing in southern California in 1950’s.
California was previously Mexico where little of any English was previously spoken prior to Statehood. Spanish in Mexican dialect and various Native Indian languages were the language of residents prior to the Europeans in California. Hence, there were no Anglo terms or syntax such as “Santa Ana” divided or English words like “Winds” used by historical locals to describe the destructive winds they also experienced leading up to their name for such winds. The Anglo term “Santa Ana Winds,” the town of Santa Ana, California, and the city of Santa Ana, California did not yet exist when the term “Santana Winds” translated from “Vientos Santana” was being uttered by English speaking persons in California to describe southern California’s dry, strong winds.
The reference to the City of Santa Ana is incorrectly attributed and coincidence a result of person mis-atrributing the wind name “Santanas” to a small location or small area where the winds also occurred. Many who could locate and identify with the area of Santa Ana in Orange County, California falsely believed the winds were in reference and based upon the town and city merely, because the dry winds were known to be in that area. Persons who identified with the town and city of Santa Ana as the (false) basis for the name of “Santa Ana Winds” were probably unfamiliar with the fact the winds existed and were started elsewhere outside of the Santa Ana, California area, or these persons may not have been nor had family members native to the southern area of California. Additionally, travel was not mainstream, not as affordable, nor as convenient at that time when the myth that the town and City of San Ana was the same or the result of the “Santana Winds.” It is also suspected these persons were also unaware the original term’s translation from the Spanish/Mexican’s original phrase “Vientos Sanatana,” was “Devil Winds” and “Santana Winds” not “Santa Ana” thereby creating a false perception and mis-application that the city of Santa Ana was named in or around 1869 from the winds or the winds were named because of the city when the reference “Santa Ana” did not yet exist for the winds.
The destructive, dry winds do not merely blow in the smaller area of Santa Ana or it’s easterly mountains or area. The winds are also in, for example, Campo, Carlsbad, Fallbrook, Pauma, Point Loma, San Diego, at the United States border with Mexico, Los Angeles, Riverside, Azusa, Malibu, south and south east in Mexico, north into Ventura County, all nowhere in proximity to what is now called the city of Santa Ana and the Santa Ana mountains. Any relation to the town or city of Santa Ana is made up and a false attribution of the Spanish/Mexican term “Vientos Santana” and its original English translation used in California “Santana Winds.”
It’s coincidence one area that has Santana Winds is the city of Santa Ana. Moreover, “Santa Ana” was not in use as the term for the dry, strong winds at the time the area and city of Santa Ana was named, founded in 1869. The term still in use then and widely utilized until approximately the 1950s was “Santana Winds” according to local newspaper reporting.
The original authentic translation to describe the destructive, dry, strong, winds was somewhat “dumbed down,” as new age persons sometimes use to describe such things or so to speak. The destruction of the original translation of “Vientos Santana” to “Santana Winds” from Spanish/Mexican into “Santa Ana Winds” came about locally and spread as local Anglo persons became employed to distribute verbal reporting of weather reports as opposed to written reports about these winds and the harm the winds caused. These reporters, weatherpersons, and airway news stations personnel, not always having a Mexican accent, not understanding the term completely or how to pronounce it properly, but rather being Southern California accent neutral, mispronounced “Santana” into “Santa Ana” to viewers and communities in an attempt to enunciate all the letters in an Anglo style of “Santana” as broadcasting taught.
Thereafter, Californias and others hearing the mispronounced word on broadcasts, began to believe “Santana” was an incorrect pronunciation and came to perceive “Santa Ana” was the correct proniucation when it was not. As a result of relying in the perceived authority and perceived expertise of the audio reporters, viewers also began mispronouncing “Santana Winds” into “Santa Ana Winds.” Hence, this caused the destruction of the actual original translation of “Santanas” placing emphasis on Saint (Santa) Ana. The Latin/Mexican term more emphasized the Santana or Satan portion of the term.
The original term “Vientos Santana” and translated to “Santana Winds” was never meant to emphasize Satan in a respectful manner by capitalizing and splitting from Santana to Santa Ana as Caucian California’s began to do. Mexico had become a Roman Catholic country fearing the devil and Santana which is Spanish/Mexican for Devil. Hence, to capitalize and divide into a title Santana into Santa Ana and thereby give respect to Satan’s name would not have been prompted in translating Vientos Santana to Sant Ana Winds in California it is deduced.
As of April 2018, in California and Mexico, the destructive, dry winds are still referred to as “Santanas” and “Santana Winds” instead of “Santa Anas” or “Santa Ana Winds” by not only those of Mexican heritage, but by some locals knowing the original and correct translation was altered into “Santa Ana’s” in error.
The Santa Ana winds are commonly portrayed in fiction as being responsible for a tense, uneasy, wrathful mood among Angelenos. Some of the more well-known literary references include the Philip Marlowe story "Red Wind" by Raymond Chandler, and Joan Didion's Slouching Towards Bethlehem.
...[T]he violence and the unpredictability of the Santa Ana affect the entire quality of life in Los Angeles, accentuate its impermanence, its unreliability. The wind shows us how close to the edge we are.