A snow-fire bridge mechanism for the 2025 Southern California winter wildfire

In January 2025, a rare and highly destructive wildfire devastated Southern California, becoming the costliest wildfire event in recorded history. The unusual timing of this wildfire suggests the possibility of unique remote, large-scale climatic precursors that differ from those of previous wildfires. Here, through observational analysis and large-ensemble numerical simulations, we identify that western Eurasian snow cover reduction is associated with weather conditions favorable for wildfires in Southern California in December-January, and simulations indicate that this can occur via an atmospheric teleconnection from western Eurasia, across the North Pacific and into North America. Both observations and simulations show that the reduced snow cover over western Eurasia contributes to the typical wintertime western warming-eastern cooling dipole pattern in North America. The main dynamical mechanisms involve downstream propagating Rossby wave trains triggered by the reduced snow cover in western Eurasia, as well as wave-mean flow interaction over the North Pacific. Our study suggests that Eurasian snow cover anomalies can be predictively linked to both subsequent wildfire risk in California and the wintertime North American zonal dipole temperature pattern, highlighting the broader impacts of Eurasian cryosphere variability on remote climate extremes.