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California fires: What are the Santa Ana winds?

California fires: What are the Santa Ana winds?
Posted at 1:29 PM, Dec 06, 2017

Dry conditions and the Santa Ana winds are being blamed for at least five fast-moving wildfires that have burned more than 65,000 acres in Southern California.

The term "Santa Ana winds" gets thrown around a lot by Southern California meteorologists and even shows up in "I Love L.A.," Randy Newman's classic ode to Los Angeles.

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But what are they, exactly?

The National Weather Service defines the Santa Ana wind as "a weather condition in which strong, hot, dust-bearing winds descend to the Pacific Coast around Los Angeles from inland desert regions."


The winds often pass through Santa Ana Canyon, east of Los Angeles; thus the name.

The weather condition is most common in the period of October through March when the desert is relatively cold, and the winds develop as high pressure builds over the Great Basin in Nevada, according to the UCLA Department of Atmospheric and Oceanic Sciences.

As the cold air there begins to descend, it's forced downslope toward the Pacific Ocean, causing it to compress and warm as it falls. The air starts out dry, but the relative humidity decreases as the temperature increases, causing the air to end up even drier once it reaches sea level.

The air gains speed as it goes through passes and canyons. The result is the strong, hot Santa Ana winds, which increase the potential for wildfires by drying out vegetation. The winds also accelerate the speed of wildfires once they start.

According to a report from the Southern California Geographic Coordination Center, multi-day Santa Ana wind events aren't uncommon during the winter months. The highest number of wind days occur in December and January. Both months also see the highest number of days with moderate to strong wind events.