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Exploring the beautiful nature of California


California Nature: Santa Ana Winds


Named after Southern California's Santa Ana Canyon and a fixture of local legend and literature, the Santa Ana is a blustery, dry and warm (often hot) wind that blows out of the desert. Local legends associate the hot, dry winds with homicides and earthquakes, but these are myths.

Another popular misconception is that the winds are hot from their desert origin. Actually, the Santa Anas develop when the desert is cold, and are most common during the cool season stretching from October through March. High pressure builds over the Great Basin and the cold air there begins to sink. However, this air is forced down slope which compresses and warms it at a rate of about 29 degrees F per mile of descent. As its temperature rises, the relative humidity drops; the air starts out dry and winds up at sea level much drier still. The air picks up speed as it is channeled through passes and canyons.
Santa Ana winds in Southern California The Santa Ana winds occur mainly in the fall season with wind gusts from 35 mph to 45 mph. These furious and sometimes deadly force winds move from the East to the West across the state of California.

Beginning with a pocket of high pressure air, the wind moves through the states of Nevada, Utah and Arizona pushing the air up, up and up and then over The San Gabriel Mountains. This air then accelerates down the west side of The San Gabriel Mountains, gaining tremendous speed as it goes through the canyons often reaching hurricane force winds. Although the Santa Ana winds originate as colder air over the high desert, they arrive in Southern California as hot air because of the difference in elevation. Air temperature is strongly correlated to elevation, and if there was not a dramatic difference in elevation between the Great Basin and the Los Angeles Basin, the Santa Ana winds would reach Southern California as cool winds. When air drops in elevation, however, it becomes compressed and warmer. This is called adiabatic warming. .
Santa Ana winds are usually dry winds, which further exacerbates the potential danger of wildfires. As the air descends and warms due to compression, its relative humidity decreases. Relative humidity can drop below 10% during a Santa Ana wind event. Because of the low relative humidity, this hot, fast-moving air can literally strip already dry vegetation of whatever little moisture it may have, further increasing fire danger.

The wind also picks up dust, and during Santa Ana wind events, dust plumes carried by strong offshore winds can be seen over the ocean from space.

When a high pressure system develops over the Great Basin to the north and east of Southern California, prevailing winds push the air in a clockwise direction around the high pressure. Santa Ana winds are caused by this phenomenon, especially when lower pressure to the west actually pulls the air across Southern California in strong offshore winds.
The Santa Ana winds can cause fog and increase wildfires 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 protected 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 happens when a ground fog settles in Southern California during the end of a Santa Ana wind episode. The Santa Ana condition will be 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 "Santa Ana fog"  constitutes an example of an air inversion.
While characteristically hot and dry, the Santa Anas can also blow cold and dry, and in fact can bring some of Southern California's coldest weather.  High cloudiness, most commonly cirrus and altostratus clouds, may be observed, and on rare occasions these usually dry southwest-flowing winds can bring rain.

Santa Anas can cause a great deal of damage. The fast, hot winds cause vegetation to dry out, increasing the danger of wildfire. Once the fires start, the winds fan the flames and hasten their spread. The winds create turbulence and establish vertical wind shear (in which winds exhibit substantial change in speed and/or direction with height), both posing aviation hazards. The winds tend to make for choppy surf conditions in the Southern California Bight, and often batter the north coast of Santa Catalina Island, including Avalon cove and the island's airport.
 
 
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