ECSS2023-106
https://doi.org/10.5194/ecss2023-106
11th European Conference on Severe Storms
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Revisiting the unusual period of F4/F5 tornadoes in Europe from 1965 to 1971

Jerome Schyns1, Christoph Gatzen2, and Lisa Schielicke1,2
Jerome Schyns et al.
  • 1University of Bonn, Institute of Geosciences, Department Meteorology, Bonn, Germany
  • 2Freie Universität Berlin, Institut für Meteorologie, Fachbereich Geowissenschaften, Berlin, Germany (lisa.schielicke@met.fu-berlin.de)

In the six-year period of 1965 to 1971, an unusually high number of violent tornadoes of category F4 and F5 was observed in Europe including six F4 tornadoes in Switzerland, France (2), Italy (2) and Germany as well as one F5 tornado in France. We use this tornado series to analyze the conditions present in violent European tornadoes.

ESWD (European Severe Weather Database) data, ERA5 reanalysis data and historic weather maps are used to classify the large-scale weather patterns with respect to the strength of synoptic-scale forcing, the position of the jet stream across Europe and relative to the tornadic thunderstorms, location of fronts including drylines, coastal fronts, and pre-frontal convergence zones that could have influenced the thunderstorms development. We use an ingredients-based method to analyze the large-scale flow, focusing on the origin and advection of lapse rates, low-level moisture, zones of lift, and vertical wind shear. For example, we distinguish between situations with a large area affected by an overlap of CAPE and strong vertical wind shear and situations where only a small “sweet spot” could have influenced the development and organization of the thunderstorms.

The vertical profile close to the convective storms are analyzed in ERA5 data that are compared with observation data. Here, we concentrate on the profile of vertical wind shear and the occurrence of low-level streamwise vorticity, expected cloud base, and expected cold pool potential due to evaporative cooling. Additionally, we estimate the motion vectors of supercells.

Proximity soundings serve to initialize supercell simulations using cloud model 1 (CM1, using the pre-configured, idealized supercell set-ups). We discuss the development of convection in the idealized model simulation and characterize the thunderstorms with respect to the lifted condensation level, the height of the mesocyclone, storm motion vector, and col pool potential. The results are compared to findings from the literature.

How to cite: Schyns, J., Gatzen, C., and Schielicke, L.: Revisiting the unusual period of F4/F5 tornadoes in Europe from 1965 to 1971, 11th European Conference on Severe Storms, Bucharest, Romania, 8–12 May 2023, ECSS2023-106, https://doi.org/10.5194/ecss2023-106, 2023.