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This study explores the early-winter atmospheric response to Ural blocking anomalies in November, using a nudging technique to constrain the temperature and dynamics in a high-top atmospheric model. Persistent Ural blocking anomalies in November are associated with a warm Arctic/cold Siberia pattern and increased upward planetary waves entering the stratosphere, leading to a warming of the polar vortex. This stratospheric response then propagates in the troposphere, leading to increased occurrence of the negative North Atlantic Oscillation in December and January. In contrast, simulations with perturbed Barents-Kara sea ice and Siberian snow in November do not reproduce a significant atmospheric response. In simulations including a slab ocean, the Ural blocking induces Barents-Kara sea ice and Siberia snow anomalies that resemble composite analyses from observations. These results highlight Ural blocking variability in November as a robust driver of early-winter stratospheric warming while questioning causality between sea ice/snow and Ural blocking anomalies.

Plain Language Summary The polar stratosphere is a source of climate predictability, especially stratospheric warmings that are followed by extreme weather events in midlatitudes. In autumn, sea ice loss in the Barents-Kara sea, as well as excess of snow over Siberia, have been found to drive stratospheric warmings by enhancing large-scale planetary waves propagating into the stratosphere. Barents-Kara sea ice anomalies have also been suggested to force the recent trend toward cooler wintertime temperature in Siberia. A high over western Siberia, or Ural blocking pattern, is a key signal in the chain of mechanisms that explains the link between sea ice/snow anomalies, cooler Siberia, and the stratosphere. In this study, a persistent Ural blocking in November is directly imposed in an atmospheric model. Robust responses are found: a cooling over Siberia, an increase in upward planetary waves, and a warming of the polar stratosphere in early winter. In contrast, imposing November Barents-Kara sea ice and Siberian snow anomalies does not lead to any significant atmospheric response in the model. These findings question the causality between November sea ice/snow and Ural blocking anomalies while highlighting persistent Ural blocking conditions as a source of predictability of the Northern Hemisphere climate.