Tornado occurrence and characteristics in Central Europe under different synoptic conditions

While mesoscale processes are generally associated with the development of severe convective events, it is the synoptic situation that creates the environment for convective events. Thus the knowledge of the synoptic and mesoscale conditions are crucial for forecasting such events, while statistical analyses are helpful for raising a general awareness of the possibility of severe convective events. Beyer et al. 2025 recently performed a statistical analysis of the occurrence of tornadoes in Germany. This study is now expanded with the goal of analysing the occurrence and characteristics of tornadoes under different synoptic conditions.

The study is based on data from the European Severe Weather Database (ESWD), with 1812 confirmed tornado reports within Germany from 1940 to 2024, together with an automatic classification of synoptic patterns. The automatic method, GWL-REA, is broadly based on a pattern correlation method using ERA5 reanalyses, with various optimizations and AI-based enhancements. Four meteorological variables are used for the inputs: mean-sea-level pressure, geopotential height at 500 hPa, 500–1000 hPa relative thickness and the total column precipitable water. Classifications are available from 1940 up to the present. The most widely used set of circulation patterns are the 29 Hess–Brezowsky Grosswetterlagen (GWL) for Central Europe. These are intuitively defined and named patterns which are in common use amongst synoptic meteorologists. They have been used e.g. in a study of thunderstorms under different synoptic patterns by Wapler and James (2015). The classification has since been slightly updated: The pattern BM (Zonal Ridge across Central Europe) has been split into an anticyclonic (BMa) and a cyclonic (BMz) representation. This yields 30 synoptic patterns.

 

The analysis reveals conditions favourable for tornadic storm development and highlights regions affected under different flow regimes. Additionally, the analysis shows that different synoptic conditions are typically associated with specific tornado characteristics, such as the direction of movement or tornado severity. These relationships can be explained meaningfully via a description of the synoptic-meteorological characteristics of each weather pattern.

 

The Grosswetterlagen Wz (Cyclonic Westerly) and SWz (Cyclonic South-Westerly) have been identified as patterns inducing the most tornadoes over Germany. Wapler and James (2015), found that the Grosswetterlagen most frequently associated with thunderstorms are Sz (Cyclonic Southerly), SEa (Anticyclonic South-Easterly), SWz (Cyclonic South-Westerly), TrW (Trough over Western Europe) and TB (Low over the British Isles).