A common weather phenomenon in southern California throughout autumn and winter are the Santa Ana winds. Santa Ana winds are a katabatic wind, a type of \"drainage\" wind that carries air from a higher elevation down a slope under the force of gravity. Santa Ana winds are a hot and dry in nature, blowing from the elevated interior regions of southern California towards the coastline. The most notable impacts of the Santa Ana winds are their ability to quickly spread fires, blow dust and cause power outages.

The origin of the Santa Ana name comes from the fact that these winds blew intensely through the Santa Ana Canyon, affecting early settlers of the area. Newspaper references to Santa Ana winds date back to 1882.

These winds usually develop when a large ridge of high pressure develops over the Great Basin and the upper Mojave Desert in Nevada and interior Southern California. The clockwise wind flow around theses high-pressure systems brings an east-to-west wind to the highly populated areas between San Diego and Los Angeles.

As these winds surge towards the coastline, they flow down the slopes of the San Gabriel, Santa Ana and the San Bernardino mountains. As wind flow pushes down these mountain ranges, the air is compressed and as pressure increases, temperature also increases resulting in the air mass warming.

With the compression and warming, much of the moisture is removed from the fast-moving airmass. The relative humidity within these winds often drops below 20 percent, helping to dry out vegetation in the path of the winds which ripens fuel for wildfires and leads to blowing dust. Temperatures can soar into the mid-80s and lower 90s during these events. However, some Santa Ana events in winter don't always produce such a major temperature spike.

The hot, dry nature of these winds, combined with gusts anywhere from 35 to 55 mph, create a hazardous wildfire potential. The brisk winds can quickly fan the flames of any ongoing or developing wildfire, making it difficult for firefighters to get control of the blazes that erupt during Santa Ana events. The Santa Ana winds are associated with some of California's largest and deadliest wildfires like the Cedar Fire in 2003 and the Laguna Fire in 1970.
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\r\nWhen the Santa Ana winds eventually reach the Pacific Ocean, they usually result in choppy surf conditions along the coastline. The winds can also generate large waves that affect Catalina and Santa Cruz Islands.

Highest gusts within these winds are often observed during the overnight and morning hours, when the onshore sea breeze is dormant and not acting against the Santa Ana winds. Mountain passes including Soledad Pass, Cajon Pass and the San Gorgonio Pass are all known for seeing high winds during Santa Ana events. 
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\r\nImage: Wildfires fanned by Santa Ana winds burn across southern California on October 28, 2003, including the Cedar fire east of San Diego. (NASA Terra/MODIS True Color)