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Santa Ana Winds Spreading Southern California Fires - LEX18.com | Continuous News and StormTracker Weather

Santa Ana Winds Spreading Southern California Fires

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Fires are raging in Southern California, despite the fact that their water year (wet season) began over two months ago. In fact, Los Angeles has acquired only 0.11” of rainfall since October 1st. That puts it at the 11th driest start of the water year since records have been kept. This doesn't help the fire situation. Conditions and soil are so dry that even just hot temperatures can spark a flame; and all it takes is one tiny flame.


Fires encroaching on the 405 Freeway in Southern California. (Image Courtesy: LA Times)

What also doesn't help is the weather. Conditions across the country right now have a large heat ridge in place over the west coast. This is also responsible for all of the cold air diving south. Usually when one half of the country experiences a ridge of warmth, the other is cooler and receiving more precipitation.

With this large ridge over the Eastern Pacific, comes smaller areas of stationary high pressure. When lined up in the right spot, these high pressure centers can cause offshore wind in Southern California. When this happens, the phenomenon is called the “Santa Ana” winds.

The Santa Ana are a katabatic wind that flows down slope of the usual windward side of the Transverse Range in Southern California. As air descends it warms, dries, and picks up speed. Nothing in that combination is good for wildfires. Wind speeds can often reach 25-50 mph with gusts even higher.

The Santa Ana winds are tend to warm up the cities at the base of the Transverse Ranges. 

The fires in Southern California are experiencing wind speeds of 25-35 mph with wind gusts to 60. Isolated gusts are reaching as high as 90 mph at times. One particular fire has destroyed over 100 homes in Ventura County and more will be threatened as long as the Santa Ana winds continue. A separate fire has shutdown a portion of the 405 Freeway near Bel Air, which connects West Los Angeles with the San Fernando Valley.

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The same process is seen in other parts of the world, but in smaller scenarios. A unique version of dry adiabatic wind forms in the Chetco River Valley of Southwestern Oregon. As the wind flows down into the river valley it warms and will funnel all the way to the Pacific Ocean. When it reaches the Pacific, it only warms up the city of Brookings, OR and a few surrounding communities. Temperatures can run warmer in Brookings by 15-30 degrees compared to just a few miles north or south of the opening of the river.

Santa Ana winds are not to be confused with Foehn or Chinook Winds. The process is the same, but Foehn winds happen on the leeward side of a mountain.

-Meteorologist Seth Phillips

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