Circulation Pattern Associated With Record 2025–26 North American Winter May Become More Common

Abstract

The 2025–26 late‐fall and winter climate pattern featured an extreme upper‐tropospheric zonal geopotential height gradient across North America, consisting of an amplified west ridge and an east trough, which produced record warmth and low snowpack across the western United States alongside severe cold and winter storms in the east. The dynamical origins of such extreme ridge‐trough patterns and whether their underlying circulation configurations are becoming more or less frequent under anthropogenic warming remain unresolved. Using ERA5 reanalysis and the CESM2 Large Ensemble, we find that the extreme ridge‐trough pattern was associated with convective suppression in the eastern tropical Pacific, consistent with a Gill‐type upper‐tropospheric response and a poleward‐propagating Rossby wave train that manifests as a zonal geopotential height gradient. We train a self‐organizing map on the joint 250 hPa streamfunction and outgoing longwave radiation anomalies and find that the convective‐circulation pattern over the eastern Pacific and North America sector, reminiscent of the 2025–26 extreme ridge‐trough pattern, increases in frequency by the end of the 21st century, despite a decrease in amplitude of the composite scalar defining the ridge‐trough pattern. The covariance between eastern tropical Pacific convection and the upper‐tropospheric circulation over the western United States also strengthens. This study suggests that the background state under anthropogenic warming increasingly favors the convective‐circulation pattern associated with the 2025–26 extreme ridge‐trough pattern.