Tornadoes in Germany 1950–2003 and their relation to particular weather conditions

Abstract

The objective of this statistical-climatological study is to identify characteristic weather situations in which tornadoes in Germany preferably occur. Tornado reports have been taken from the TorDACH database for the period 1950-2003. Weather situations are defined by the objective weather types classification of the German Meteorological Service (DWD), described by the direction of air mass advection, the cyclonality and the humidity (precipitable water) of the troposphere. In addition the number of thunderstorm days and aerological parameters, derived from temperature and dewpoint in 850 and 500 hPa, are taken into account.Higher frequencies of tornadoes in Germany are found in recent years 1998-2003, particularly in the years 2003 (40 tornadoes) and 2000 (warmest year in Germany since the beginning of the 20th century). There is no shift of the seasonal cycle detectable for the period 1980-2003 compared to 1950-2003 and also no shift of the intensity distribution. The majority of the tornadoes can be attributed to 3 specific weather types, all with a south-westerly advection and high humidity. This can be found for weak as well as for strong tornadoes. Anti/cyclonality in 950 hPa reduces/enhances the tornado frequency roughly by a factor of 2, while in 500 hPa cyclonality shows no significant influence.The fraction of the number of registered tornado days to the number of thunderstorm days has a maximum of one tornado in 50 thunderstorm days in the north-western part of Germany. Specific ranges of temperature and dewpoint in 850/500 hPa, which are not the highest values, are favoured for the occurrence of tornadoes.

The spatial distribution of severe convective storms and an analysis of their secular changes

“…Concannon et al (2000) found large variability between different periods in the record of strong and violent tornadoes in the USA. In their analysis of tornadoes in Germany, Bissolli et al (2006) reported no shift of the seasonal cycle detectable for the period 1980-2003 compared to 1950-2003 and also no shift of the intensity distribution.…”

“…In particular, the relationship between the observed variables and tornadoes, if there is one, is not obvious. Bissolli et al (2006) combined a synoptic weather pattern analysis for Central Europe in comparison with the German TorDACH tornado reports 4 in the period 1950-2003. The synoptic pattern scheme by Deutscher Wetterdienst (DWD, the German national weather service) takes into account the direction of air mass advection, the cyclonicity and the humidity (precipitable water) of the troposphere.…”

Exceptional sequence of severe thunderstorms and related flash floods in May and June 2016 in Germany – Part 1: Meteorological background

“…Several studies have established a relationship between specific OWLK types and convective activity in terms of severe hailstorms (Kapsch et al, 2012;Mohr et al, 2015) or tornadoes (Bissolli et al, 2007). The advantages of OWLK compared to subjective methods such as the well-known classification of Hess and Brezowsky (HB, 1977) are the nonambiguous assignment criteria and the automated categorization procedure (Philipp et al, 2010).…”

Central European tornado environments as viewed from a potential vorticity and Lagrangian perspective

“…There are large and characteristic differences observed between the 15 observed tornado cases that should be kept in mind when evaluating the analysis that follows. It is known that the meteorological conditions associated with tornadoes exhibit significant seasonal variability (Bissolli et al, 2007;Romero et al, 2007;Dessens and Snow, 1989). Of the 15 cases, five occurred during the cool season (4, 5, 6, 14, and 15) and 10 during the warm season (1, 2, 3, 7, 8, 9, 10, 11, 12, and 13).…”