Abstract. During a 15-day episode from 26 May to 9 June 2016, Germany was affected by an exceptionally large number of severe thunderstorms. Heavy rainfall, related flash floods and creek flooding, hail, and tornadoes caused substantial losses running into billions of euros (EUR). This paper analyzes the key features of the severe thunderstorm episode using extreme value statistics, an aggregated precipitation severity index, and two different objective weathertype classification schemes. It is shown that the thunderstorm episode was caused by the interaction of high moisture content, low thermal stability, weak wind speed, and large-scale lifting by surface lows, persisting over almost 2 weeks due to atmospheric blocking.For the long-term assessment of the recent thunderstorm episode, we draw comparisons to a 55-year period regarding clusters of convective days with variable length (2-15 days) based on precipitation severity, convection-favoring weather patterns, and compound events with low stability and weak flow. It is found that clusters with more than 8 consecutive convective days are very rare. For example, a 10-day cluster with convective weather patterns prevailing during the recent thunderstorm episode has a probability of less than 1 %. IntroductionBetween the end of May and mid-June 2016, Germany and large parts of central and southern Europe were affected by an exceptionally large number of severe convective storms and related extremes such as heavy rainfall, hail, and tornadoes (Fig. 1). Rain totals exceeding 100 mm within a few hours at several locations in Germany triggered various flash floods and floods mainly in small catchments. In the town of Braunsbach in the federal state of Baden-Württemberg, for example, a severe flash flood on 29 May with a height of up to 3.5 m caused serious damage to more than 80 buildings, of which five were completely lost (Daniell et al., 2016). Only 3 days later on 1 June, extreme rain in the district of Rottal-Inn in the south of Bavaria evoked a sudden and dramatic rise in the levels of several creeks such as the Simbach, where the height increased from 20 cm to more than 5 m within only 12 h. Subsequently, the village Simbach am Inn experienced the largest flooding in history. Some of the thunderstorms during the 2 weeks also produced hail with diameters between 0.5 and 5 cm. A total of 12 tornadoes in 8 days with intensities between F0 and F1 on the Fujita intensity scale, were recorded and confirmed by the European Severe Weather Database (ESWD; Dotzek et al., 2009).The severe thunderstorms caused substantial damage to buildings, infrastructures, transportation networks, and crops. A large number of roads and railroads were blocked or severely damaged, and some villages experienced power outPublished by Copernicus Publications on behalf of the European Geosciences Union.

Abstract. Comprehensive lightning statistics are presented for a large, contiguous domain covering several European countries such as France, Germany, Austria, and Switzerland. Spatiotemporal variability of convective activity is investigated based on a 14-year time series (2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014) of lightning data. Based on the binary variable thunderstorm day, the mean spatial patterns of lightning activity and regional peculiarities regarding seasonality are discussed. Diurnal cycles are compared among several regions and evaluated with respect to major seasonal changes. Further analyses are performed regarding interannual variability and the impact of teleconnection patterns on convection.Mean convective activity across central Europe is characterized by a strong northwest-to-southeast gradient with pronounced secondary features superimposed. The zone of maximum values of thunderstorm days propagates southwestward along the southern Alpine range from April to July. Diurnal cycles vary substantially between both different months and regions, particularly regarding the incidence of nighttime lightning. The North Atlantic Oscillation (NAO) is shown to have a significant impact on convective activity in several regions, which is primarily caused by variations of the largescale lifting pattern in both NAO phases. This dynamical effect is partly compensated for by thermodynamical modifications of the pre-convective environment. The results point to a crucial role of large-scale flow in steering the spatiotemporal patterns of convective activity.

The driving factors that influence the spatial and annual variability of thunderstorms across Europe are still poorly understood. Due to a lack of long‐term, reliable and consistent information about the occurrence of convective storms, a weather type classification has been developed that estimates thunderstorm probability from a combination of appropriate meteorological quantities on the mesoscale. Based on this approach, the temporal and spatial variability of convection‐favouring environments is investigated between 1958 and 2014 using a high‐resolution reanalysis dataset. To identify potential drivers for convective days, typical upper‐level flow patterns were deduced using a multivariate approach. Our results suggest a strong link between local‐scale thunderstorm activity and large‐scale flow and air mass properties, such as stability, moisture, or vertical lifting. For example, while all over central Europe the most prominent pattern is given by a southwesterly flow type over the respective area, distinct regional discrepancies regarding further favourable flow types are observed. The crucial role of large‐scale flow is further studied by assessing the relation between Northern Hemisphere teleconnection patterns and widespread convective activity. It is found that positive phases of the East Atlantic or Scandinavian patterns go along with a significant enhancement of convection‐favouring conditions in several European regions, which can be explained by anomalies in the large‐scale temperature and flow fields. Sea‐surface temperature over the Bay of Biscay likewise impacts the convective environment, with the largest positive effect over the western part of the study area.

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