Role of the stratosphere in the January 2025 Pan-Atlantic Event: A Case Study of Storm Éowyn

Storm Éowyn made landfall in the British Isles on 24 January 2025, becoming one of the most devastating extratropical cyclones in recent years with average wind speeds exceeding 39 m/s. This storm, following record-breaking low temperatures and snowfall in the Southern United States, constitutes a Pan-Atlantic cold and windy compound extreme. Given the widespread impacts of these compound extremes, identifying their atmospheric precursors is critical for improving predictability and preparedness.

The stratosphere played an important role in the January 2025 Pan-Atlantic event. We demonstrate how a strong stratospheric polar vortex, in conjunction with tropospheric drivers like the Alaskan Ridge weather regime, facilitated enhanced southward cold air advection in North America and the intensification of cyclone Éowyn over the North Atlantic. This case study provides an archetype for future compound Pan-Atlantic cold-windy events and outlines possible pathways for improved sub-seasonal forecasting.