Southern California is entering the season when Santa Ana winds typically occur, bringing dry conditions that can disrupt travel and elevate wildfire risks. Those winds can make travel difficult, topple trees, and fuel wildfires.
While the ocean breezes along the West Coast are commonly perceived as cooling the area, Santa Ana Winds blow in the opposite direction.
They start inland, near the dry interiors of the southwest U.S. As they move through mountain passes and valleys, they gain heat.
Therefore, conditions can become very hot, extremely dry, and fast-moving. These windy conditions typically affect weather patterns throughout Southern California from September to May.
The strongest winds often arrive before the fires
Santa Ana Winds are able to produce several types of weather-related issues in the Southland prior to potentially causing wildfires. According to the National Weather Service, downslope wind events like Santa Ana Winds can exceed 40 mph, with stronger gusts creating hazardous driving conditions.
The American Association of Geographers notes that Santa Ana Winds have shut down traffic on major highways across Southern California.
With gusts approaching 80 mph (129 km/h), the same organization reports that Santa Ana Winds have caused dust storms, stripped moisture from topsoil, and damaged structures and vehicles.
The strong winds have also overturned large vehicles such as semi-trucks. The falling tree branches and flying debris add another hazard for drivers and residents alike.
Their contribution to wildfire development receives the majority of media coverage.
Santa Ana Winds occur during the autumn wildfire season in Southern California, when dry conditions already increase fire danger.
One brushfire grew far beyond its starting point
In October 2023, Santa Ana Winds assisted in growing the Highland Fire in Southern California.
A relatively small brushfire grew from approximately 14 acres to more than 2,400 acres before being contained roughly a week later after expanding across the landscape.
The journey begins far from the California coast
Santa Ana Winds form due to high pressure developing over elevated desert regions and mountainous areas of the western United States. The National Weather Service explains that Santa Ana Winds form when air moves from a region of high pressure over the dry desert Southwest toward lower pressure off the California coast.
The air flowing from the high-pressure region toward the low-pressure region flows westward.
Upon descending through mountain passes and lower elevation areas, the air compresses and warms. Meteorologists refer to this process as adiabatic warming.
Due to sinking, there is no external source of energy providing heat to the air.
According to the American Association of Geographers, temperature increases approximately 5.5 degrees F per thousand feet of descent.
Consequently, by the time Santa Ana Winds reach lower elevation areas, temperatures can rise to nearly 100 degrees F. For this reason, Santa Ana Winds feel unusually warm despite generally occurring during cooler months of the year.
Dry air is what turns them into a wildfire threat
While the temperature increase associated with Santa Ana Winds is noteworthy, it is only one aspect of these windy conditions. Santa Ana Winds are also uniquely dry.
When Santa Ana Winds arrive in Southern California, humidity levels drop below 10%. Vegetation loses moisture rapidly under these conditions.
Many native plant species have adapted to dry conditions, according to the American Association of Geographers. Non-native grasses and vegetation often struggle during extended droughts.
A 2019 study by climate researchers projected future Santa Ana wind declines using climate models.
However, a 2021 study found that ‘cold’ wind variants carry lower wildfire risks than ‘hot’ ones.
Researchers involved in the study believe their work will eventually help improve early warning systems and better prepare Southern Californian communities for severe wind events.
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