December 10, 2024
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How Santa Ana winds cause Malibu fires
Dry weather and extreme wind events in Santa Ana contributed to the explosive growth of the Franklin Fire in Malibu, California.
A firefighter pulls a water hose as the Franklin Fire burns a palm tree near a building in Malibu, California, Dec. 10, 2024.
The Franklin Fire, which broke out Monday night north of Pepperdine University in the Malibu area of Los Angeles County, quickly grew in size within hours due to extremely dry weather and the region’s notorious fire intensity. It expanded and burned more than 2,200 acres. Santa Ana wind.
Santa Ana winds are a common cause of fast-growing and damaging fires in the region because they can fan and spread fires quickly. Some wind gusts reached more than 80 mph near the fire.
Santa Ana winds are the result of a specific meteorological setting. “Typically what happens is that the low pressure system rises over California into Washington and Oregon and then moves south through Nevada and Arizona.” said Mike Wofford, a meteorologist at the National Weather Service office in Los Angeles. “We call this an ‘inside slider.'” As that low pressure moves out, an area of high pressure moves behind it. “High pressure over Nevada and low pressure over California drive the wind,” Wofford explains. “Because the wind changes from high to low.”
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The greater the difference between high and low ground, Wofford said, the faster the winds will move. The high pressure system over Nevada is currently relatively strong. As the winds head toward Southern California, they flow through many narrow mountain canyons. This causes the wind to move faster. “It’s like squeezing a balloon and letting the air out,” Wofford says. (In fact, the Santa Ana winds get their name from the Santa Ana Valley, which lies between the Santa Ana Mountains and the Chino Hills.) Wind gusts in excess of 110 mph have been reported in some areas in the mountains around Los Angeles. Wind gusts of 93 mph were recorded on the Magic Mountain Track Trail. The current wind phenomenon is similar to one in early November that fanned the flames of a wildfire that destroyed hundreds of buildings in Ventura County.
Winds are common in Santa Ana this time of year, but yesterday and today’s wind speeds were unusually strong. And being hot and dry in nature, these winds can also especially help fuel fires. As the wind blows downhill over the desert, the air becomes compressed and warms, while also drying out the air. These dry winds can further dry out already dry plants and even ignite them from the slightest spark.
“Even in a normal year, we’re barely a desert,” Wofford said. The vegetation in the area where the Franklin Fire occurred was already dry after months of little rain. Typically, the region’s hot, dry summers are followed by cold season rains that reduce fire danger. However, this year’s rains have not yet begun in the region.
Forecasters had issued a red flag for “particularly hazardous conditions” for the region from Monday night into Tuesday afternoon due to windy and dry conditions. Relative humidity levels were down to 3%, Wofford said. “They’re all very crispy.”
Winds are expected to ease late Tuesday into Wednesday, but conditions are still ripe for more fires and further expansion of the Franklin Fire. Evacuation orders have been issued for parts of the coast, as well as parts of the Pacific Coast Highway and schools in Malibu. Currently, the fire suppression rate is 0%.
