Understanding Winter Windstorm Predictability over Europe

Abstract. Winter windstorms are one of the most damaging meteorological events in the extra-tropics. Their impact on society makes it essential to understand and improve the seasonal forecast of these extreme events. Skilful predictions on a seasonal time scale have been shown in previous studies by investigating hindcasts from various forecast centres. This study aims to connect forecast skill to relevant dynamical factors. Therefore, 10 factors have been selected which are known to influence either windstorms directly or their synoptic systems, cyclones. These factors are tested with ERA5 and GloSea5 seasonal hindcasts for their relation to windstorm forecast performance. Following GloSea5 factors’ validation contributing to windstorms, the seasonal forecast skill of the factors themselves and the relevance and influence of their forecast quality to windstorm forecast quality is assessed. Factors like mean-sea-level pressure, sea surface temperature, equivalent potential temperature and Eady Growth Rate show coherent results within these three steps, meaning these factors are skilfully predicted in relevant regions leading to increased forecast skill of winter windstorms. Nevertheless, not all factors show this clear signal of forecast skill improvement for winter windstorms, and this might indicate potential for further model improvements or further understanding to improve seasonal winter windstorm predictions.