The Santa Ana winds fanning wildfires that have killed at least 25 people in Southern California and destroyed more than 10,000 houses, businesses and other structures in Greater Los Angeles are flaring up again.
Northeastern Global News interviewed Lindsay Lawrence, a Northeastern Ph.D. candidate with a master’s degree in meteorology, about the source of the Santa Ana winds, their seasonal nature—and why Southern California could experience additional extreme wind events this month.
The answers have been edited for brevity and clarity.
What are the Santa Ana winds?
Santa Ana winds are a geographically specific type of wind that occur in Southern California known as katabatic winds.
They are cold, dry, down-sloping winds that warm as they descend a mountain side.
Santa Ana winds generally blow from the east/northeast and persist due to a high pressure system over an area called the Great Basin, bordered on the south by the Mojave Desert, and low pressure off the West Coast.
Air then flows offshore through the coastal ranges of Santa Ana, Santa Monica and Laguna.
How long do the winds last?
The duration of the events definitely varies, but in January most events tend to last somewhere between two to three days.
There are, on average, five monthly SAW events during the peak season of December, January and February.
But expect up to seven or eight wind events during more active Januarys.
Did the winds arrive earlier than usual this year?
These Santa Ana winds were right on time.
The seasonality of the SAWs is such that events occur most frequently during the winter months—peaking in December and January.
This is because these months have the least sunshine and longest nights, which are essential for producing air masses over the Great Basin.
Also, these months tend to see the strongest pressure gradients across the region, which trigger the winds.
How do the Santa Ana winds contribute to wildfires?
SAWs don’t necessarily generate fires. Fires during a SAW event are dependent on a fire being ignited in the first place.
A paper that came out a few years ago shows that winds alone are insufficient when it comes to explaining burning, but 100% of fires during SAW events were human-caused, either intentional or accidental.
How do the winds hamper firefighting?
The risk of wildfire and rate at which a wildfire spreads are dependent on several environmental factors, including fuel load—flammable material, especially dry brush and trees.
Fuel load largely depends on antecedent moisture conditions, weather conditions are below normal precipitation levels or low humidity.
Other factors involve terrain and include slope steepness and the direction that the surfaces of the terrain face, as well as winds.
The Santa Ana winds, like any other strong winds during a wildfire, can push embers well beyond the present extent of the fire and enhance combustion, supplying more oxygen and making the entire fire incredibly unpredictable.
Were this year’s Santa Ana winds exceptionally strong?
Being that La Niña is currently in place, the winds might not necessarily be exceptionally strong, but La Niña has the tendency to promote wetter conditions in Northern California and anomalously dry conditions in Southern California.
The lack of rainfall in the south has exacerbated the effects of the most recent L.A. fires.
As of right now, I don’t believe there is conclusive evidence for the implications of climate change on the frequency and intensity of the SAW events.
Written by Cynthia McCormick Hibbert, Northeastern University.
