Autumn and Santa Ana Winds

Fall Means Santa Ana Winds

Annually, the onset of the fall and winter seasons brings the highest chance for Southern California’s famed Santa Ana winds. An unusually strong and persistent Santa Ana event was the largest factor in the spread of last year’s Thomas fire in Ventura (now second largest in size to Mendicino Complex). Much of Southern California experienced an on-and-off Santa Ana wind event for a little over two weeks, which contributed to the Thomas Fire burning a hot lap around Ojai and into Santa Barbara.

What Are Santa Ana Winds?

Typically Santa Ana air mass conditions are brought on by high pressure inland and lower pressure off the Pacific Coast which brings very hot and dry weather along with strong, down-slope winds.  Santa Ana winds typically happen between September and May, in the winter months. We think this UCLA FAQ outlines Santa Anas the best. In the past, the critical fire weather conditions that accompany Santa Ana winds turn the typically dry chaparral of Southern California into explosive fuel.  Some of the country’s costliest fires in history have taken place in these conditions.

Santa Ana Winds

Santa Ana Winds derive from High Pressure in the Great Basin

The Outlook This Fall

Typically, a weather event occurs by mid-September that brings moisture to regions experiencing significant fire activity which allows for the western fire season to begin to decrease in activity. All signs point to a normal seasonal progression including a transition from ENSO Neutral conditions to El Niño, therefore such an event is expected. Most regions will exit the fire season at this point, but only a brief lull is expected across California before it enters its fall fire season by October and November. Given ongoing dryness in the fuels, the fall season may very well be robust across portions of the state. Fortunately for the drought situation, Meteorologists are expecting an El Niño cycle to begin affecting the area with rains by November.  In the meantime, as the tropical air mass that has brought this summer’s rain gives way to autumn’s Pacific air mass, a few Santa Ana events should precede the El Nino’s wetting effect. 

 

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