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SALT LAKE CITY — The Santa Ana winds are expected to pick up again this week, making the Palisades and Eaton fires, among others, more difficult to contain as they continue to rage in Southern California.
High winds and red flag advisories warning of "a particularly dangerous situation" were set to activate Monday night and last through at least Wednesday, according to the National Weather Service. Winds in Los Angeles, Ventura and Santa Barbara counties could reach between 55 mph and 70 mph, with some stronger gusts at higher elevations.
"If fire ignition occurs, conditions are favorable for very rapid fire spread and extreme fire behavior, including long range spotting, which would threaten life and property," a critical red flag warning from the weather service office in Los Angeles said, per USA Today.
What are the Santa Ana winds?
The Santa Ana winds, sometimes referred to as the "devil winds," arise at higher altitudes and blow down toward sea level. The strong, dry and often warm winds blow west from Utah and Nevada to Southern California. They cause dramatic temperature increases and decreased humidity.
The winds typically form when a high-pressure system develops over the Great Basin, a large area of high desert that includes much of Nevada and parts of Utah and surrounding states, according to OpenSnow forecaster Luke Stone. The basin sits at a higher elevation than Southern California. The high-pressure systems usually form in the fall and winter but can occur at any time of year.
"Concurrently, a low-pressure system often forms off the coast of Southern California or over the Pacific Ocean. The pressure difference between the high-pressure system over the Great Basin and the low-pressure system along the coast creates a strong pressure gradient," according to Stone.
"The pressure gradient drives air from the high-pressure area in the east towards the low-pressure area in the west, resulting in winds that flow from the inland deserts towards the coast. As the air masses move westward, they descend from higher elevations of the interior mountains and deserts. The descent causes the air to compress and warm, leading to hot and dry conditions."
The narrow passes and canyons in Southern California can act as natural wind tunnels, which accelerate the wind speeds as they move toward the coast. The combination of the downslope and gap wind effects creates intense winds in the region.
Where is the wind strongest?
The windiest areas tend to be Ventura County in Los Angeles and Santa Ana in Orange County, from which the winds derive their name, Robert Fovell, a professor of atmospheric and environmental sciences at the University of Albany, told NBC News. But this year, he said, the winds were able to travel over the San Gabriel Mountains down to Pasadena and Altadena, where the Eaton Fire is located.
"It surmounted the San Gabriel Mountains, and it formed what is called a downslope windstorm," Fovell said. "That targeted the strongest winds for the foothills around Eaton Canyon."
Combined with an exceptionally dry winter, the winds created tragically ideal conditions for the fires to spread.
"The low-moisture content in the vegetation that we get in these extreme dry periods leads to these highly, highly vulnerable conditions," Mark Gold, director of water scarcity solutions at the Natural Resources Defense Council, told NBC News. "And boy, when a big Santa Ana hits, that's when the nightmare for our firefighters really kicks in."
