Investigation of a supercell merger leading to the EF4 tornado in the Czech Republic on June 24, 2021 using radar data and numerical model outputs

Abstract

An unprecedented deadly and destructive EF4 tornado struck the Czech Republic across Břeclav and Hodonín districts on June 24, 2021. On this day, several supercells developed in Central Europe, however, in Austria and the Czech Republic region only one cell produced a tornado. For this reason, in addition to the macrosynoptic setup, it is also worth exploring the small-scale cell interactions that can lead to the formation of a devastating EF4 tornado. We use ECMWF analysis and forecast fields, sounding profiles, and radar measurements to examine the synoptic weather situation and convective processes. Moreover, to investigate the evolution and structure of convection, two Weather Research and Forecasting (WRF) model simulations were carried out at 1.5 km grid spacing with onemoment and two-moment microphysical parameterizations. WRF captures the overall spatial distribution and supercellular nature of thunderstorms, although discrepancies exist in the magnitude and spatial location of individual cells. The low-reflectivity region accompanying the thunderstorms is better represented by the one-moment microphysics scheme.