Atmospheric circulation and sounding-derived parameters associated with thunderstorm occurrence in Central Europe

- In the warm season the occurrence of thunderstorms is mainly associated with a low over the North Sea and/or Scandinavia.
- In the cool season, synoptic pattern on thunderstorm days indicates a strong westerly flow and a high vertical wind shear.
- Thunderstorms are more likely when boundary layer's mixing ratios > 8 gkg-1 or vertical temperature lapse rates > 6 °C km-1.
- The best parameter in distinguishing between thunder- and non-thunderstorm days is the square root of CAPE multiplied by DLS.

The main objective of this study is to examine the influence of atmospheric circulation patterns and sounding-derived parameters on thunderstorm occurrence in Central Europe. Thunderstorm activity tends to increase as one moves from the north to the south of the research area. Maximal thunderstorm occurrence is observed in the summer months, while between October and March such activity is much lower. Thunderstorms are also more frequent in spring than in autumn. In the warm season, the occurrence of thunderstorm is associated with the presence of a trough associated with a low located over the North Sea and Scandinavia. In the cold season, the synoptic pattern indicates a strong zonal flow from the west with significantly higher horizontal pressure gradient compared to the warm season. Thunderstorms are more likely to form when the boundary layer's mixing ratios are higher than 8 g kg− 1. Deep convection is also more likely to occur when the vertical temperature lapse rates (between 800 and 500 hPa pressure layers) exceed 6 °C km− 1. During the cold season, considerably higher lapse rates are needed to produce thunderstorms. The values obtained for the convective available potential energy indicate that at least 50 J kg− 1 is needed to produce a thunderstorm during wintertime and 125 J kg− 1 during summertime. Cold season thunderstorms are formed with a lower instability but with a more dynamic wind field having an average value of deep layer shear that exceeds 20 ms− 1. The best parameter to distinguish thunderstorm from non-thunderstorm days for both winter and summer months is a combination of the square root of the convective available potential energy multiplied by the deep layer shear.