Spatial variability and potential maximum intensity of winter storms over Europe

Abstract. Extra–tropical wind storms pose one of the most dangerous and loss intensive natural hazards for Europe. However, due to only 50 years of high quality observational data, it is difficult to assess the statistical uncertainty of these sparse events just based on observations. Over the last decade seasonal ensemble forecasts have become indispensable in quantifying the uncertainty of weather prediction on seasonal time scales. In this study seasonal forecasts are used in a climatological context: By making use of the up to 51 ensemble members a broad, physically consistent statistical base can be created. This large sample can thus be used to assess the uncertainty of extreme wind storm features such as intensity or severity more accurately. In particular return periods and even a potential maximum intensity of windstorms and extra–tropical cyclones (ETCs) can be calculated depending on a specific cluster or region in Europe. A 100-year event minimum core pressure in Central Europe, for example, is estimated to be around 940 hPa, whereas it would be around 928 hPa for the British Isles. By employing extreme value statistics a potential minimum core pressure (maximum curvature) can be estimated as well. This is way below (above) a 1000-year event however, it can therefore be seen more as a physical barrier than a realistic scenario.