Mountains help create hot, dry Santa Ana winds
Several meteorological factors come together to create the hot, dry Santa Ana winds that often whip up roaring fires in Southern California.
The factors needed to stir up Santa Ana winds usually begin with a high-pressure area to the northeast of Southern California.
Winds blow clockwise around high pressure in the Northern Hemisphere, which means that winds on the southern side of the high blow from the east toward the Pacific Ocean, toward lower offshore air pressure.
The easterly winds push dry air from over the inland deserts of California and the Southwest.
The winds blow over the mountains between coastal California and the deserts. As the wind comes down the mountains, it's compressed and warms up.
As the air warms, its relative humidity drops, sometimes to less than 20% or even less than 10%. The extremely low humidity helps dry out vegetation, making it a better fuel for fires.
As the winds squeeze through canyons and valleys they speed up, fanning flames. In addition, as the winds whip over mountains and squeeze through canyons, friction helps create eddies, or swirling winds. As these come and go, the air can become almost still and then quickly speed up in gusts.
The winds are like water rushing down a very rough whitewater stream, creating eddies that come and go. These gusty winds can change direction quickly, sending flames racing into new areas.
Fires also affect the winds. Fire warms the air, causing it to rise. As this happens, more air rushes into to replace the rising air, helping create more gusts from various directions.
Source: USA TODAY research
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I grew up from ages 6 on in the Los Angeles County area. I've been in southern California for 3 weeks now on business and today I noticed the now familiar Santa Ana Winds coming off the deserts and headed out to sea. It was 93 degrees Fahrenheit where I was today. When I looked at the temperatures where I live in Northern California they were only in the mid 60s range. So, likely it is still fairly foggy up there for it to be in that temperature range this time of year. However, I had a wonderful walk along the ocean watching people play volleyball and the ocean water was likely 70s Fahernheit as I walked through it down the coast as the waves crashed to my right and I walked mostly through ankle deep foam and waves on down the coast with my wife. Beautiful Day but I'm still getting used to the warmer weather. Temperatures above 85 or even 90 only occur for about 1 or 2 days during the summer on the northern Calfornia coast most places because it makes the fog come in when it gets hot on the coast and inland during the summers there. However, if you like to surf Santa Cruz and just North of there Maverick's beach has sometimes the largest waves on the northern coast except during storms when 30 foot waves sometimes break all along the northern coast in many areas usually in a January or February storm. But this doesn't happen every year consistently.