Compound atmospheric drivers of the catastrophic 2025 Los Angeles urban firestorm

Abstract Urban firestorms are a growing hazard in fire-prone regions worldwide due to increasingly dry vegetation and expanding populations at the wildland-urban interface. In January 2025, the city of Los Angeles, California (USA), experienced an unprecedented fire disaster that destroyed over 16,000 structures and caused 31fatalities. The event was driven by a rare “jet-forced Santa Ana” wind subtype featuring an amplified upper-level ridge over the West Coast and retrograding trough over the central/eastern U.S., producing extreme northerly flow, large-scale subsidence, and mountain wave activity that impeded aerial fire suppression. While the extreme surface winds were not unprecedented, their occurrence ahead of the first winter rain was uncommon. Despite accurate multi-day forecasts, response systems were overwhelmed. Our analysis shows how upper-level atmospheric support can drive surface fire weather, compounding hazard in even well-developed areas. This underscores the importance of aligning long-range prediction with operational preparedness and communication strategies in California’s variable hydroclimate.