Abstract
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 weather-type 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 (1960–2014) 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 %.
Highlights
Between 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)
While this paper focuses on the meteorological aspects of the severe thunderstorm episode, Part 2 (Daniell et al, 2016) will discuss the impact of selected flash floods in BadenWürttemberg and will present a simplified method to estimate losses from flash floods
Since information about thunderstorm occurrence is not available over a sufficiently long period, statistical analyses are based on different proxies that estimate the convective potential of the atmosphere: large-scale weather patterns derived from reanalysis data and convective parameters obtained from vertical pro
Summary
Between 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). Another purpose of our study is to estimate empirical probability distributions with respect to the variable cluster length of days with convective weather situations using dichotomous parameters such as convectionfavoring weather types or areal-related precipitation severity index. While this paper focuses on the meteorological aspects of the severe thunderstorm episode, Part 2 (Daniell et al, 2016) will discuss the impact of selected flash floods in BadenWürttemberg and will present a simplified method to estimate losses from flash floods. The objectives of this paper are to highlight the meteorological conditions that were decisive for the thunderstorm episode, to estimate the severity of the recorded rain totals, and to put the event into historical context. Since information about thunderstorm occurrence is not available over a sufficiently long period, statistical analyses are based on different proxies that estimate the convective potential of the atmosphere: large-scale weather patterns derived from reanalysis data and convective parameters obtained from vertical pro-
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