Extreme winds are fueling horrific fires across Southern California, and one particular weather phenomenon called mountain waves is threatening to spread the flames even more.Santa Ana windsthe strong, dry winds that hit Southern California during this time of yearare especially extreme, reaching as high as 100 mph around Los Angeles. When those winds hit the San Gabriel Mountains, they can cause mountain waves.Mountain waves are these large scale patterns that occur when strong winds hit mountain ranges at a perpendicular angle, says Devin Black, a general forecaster with the National Weather Service in Oxnard, California, a city west of Los Angeles. That angle then forces the winds to rise over the mountain, and then swoop down the other side, like an ocean wave.These winds are similar to when a river flows over a large boulder, the National Weather Service explains; when the current flows over that boulder, it forms waves downstream. This creates especially gusty winds, Black says, that can cause burning pieces to jump far distances, potentially starting new fires and spreading flames.Mountain waves dont always occur during wildfires. This event is atypical and unusually strong, Black says. But when you hear this term, he adds, you should associate that with dangerous conditions, potentially.Workers attempt to remove a tree that fell on a car due to high winds in Glendale, California, on January 8, 2025. [Photo: Robyn Beck/AFP/Getty Images]Strong winds combined with drought conditionsa unique situation for Januaryhave been fueling fires across Southern California. The Palisades wildfire, which began Tuesday morning west of Santa Monica, had grown to nearly 5,000 acres as of Wednesday morning. On Tuesday evening, the Eaton fire also broke out near Pasadena; as of Wednesday morning, that had grown to more than 2,000 acres. Late Tuesday night, the Hurst fire started north of Los Angeles.Anthony Edwards, the newsroom meteorologist at the San Francisco Chronicle, has been covering the wildfires. OnMonday night, when forecasts of the potentially life-threatening wind storm began, he said on X that he was sweating bullets at work today while forecasting. This is the most concerning weather event Ive forecasted in my young career. Edwards also brought up mountain waves, saying theres a clear case of a mountain wave pattern on the Eaton Fire (and Palisades Fire to [a] lesser extent).Embers fly off a burning bus at Aveson School of Leaders elementary school during the Eaton fire in the Altadena area of Los Angeles County, California, on January 8, 2025. [Photo: Josh Edelson/AFP/Getty Images]Winds move up and over the San Gabriel Mountains, he added, and then accelerate on the opposite side in a downslope wind storm. Those gusts can reach 60 to 80 miles per hour, though Black notes that meteorologists have already recorded 100 mph winds above the San Gabriel mountains.These mountain waves have fueled some of the most destructive wildfires weve seen in recent years, climate scientist Daniel Swain said on Blueskynot only in California, but also Colorado, Hawaii, and beyond. Mountain waves also accelerate bushfires across Australia.