What is a Santa Ana weather event?

Mention the words “Santa Ana,” and people in Southern California pay close attention.

It’s a weather event that can be extremely dangerous.  Strong gusty winds dry out the air and vegetation and relative humidity drops into the single digits.  East and northeast winds blow from the inland valleys and deserts to the coast. 

The name is used because the winds blow over the Santa Ana Mountains and out to the coast from San Diego to Los Angeles counties.

A Santa Ana wind event happens when an area of high pressure sets up over the Great Basin between the Sierra Nevada and the Rocky Mountains.  In the Northern hemisphere, airs flow out and away from an area of high pressure in a clockwise direction.   Air also sinks as it flows out from the high pressure and as it travels down the mountains.  That quickly heats and dries the air.  One spark can quickly spread a wildfire out of control, especially in areas that have had little rain.

During a Santa Ana event, winds are usually stronger in the mountains and through the passes acting like air ducts sending the air from the mountains out to the oceans.

Northeasterly winds can be between 45 and 60 mph.  Some winds during previous Santa Ana events have reached 80 mph.

The Santa Ana events tends to happen between late fall and early winter, peaking in December.

The winds can be amplified when an area of low pressure is near and to the southeast of the Great Basin.  The airflow around an area of low pressure moves in a counter-clockwise direction and helps suck the air from the Great Basin.

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