Derecho radar analysis of August 11, 2017

Abstract

This paper presents an analysis of the derecho phenomenon that occurred over Poland on August 11, 2017. The storm caused 6 fatalities, 39 injuries (Mańczak et al. 202 2), and some of the greatest damage in the history of Polish forestry. Our study is based on radar meteorology and measurements from the Polish POLRAD radar network, and intended for advanced meteorologists with good knowledge of radar measurements. The research used both standard and specialized radar products as well as classic and Doppler scan data. The Doppler velocity products were especially useful for showing the characteristics of the storm. The analysis was mainly based on data from two radars: Poznań and Gdańsk, but the composite maps , consisting of data from more than one radar, were also analyzed. The derecho complex developed from unorganized thunderstorm cells over SW Poland and moved toward the NE. The various stages of the evolution of the system are presented and analyzed, accounting for the formation of a SC, the development of a rear inflow jet (RIJ), the split of the entire system, and the appearance of the bow echo signature. Significant factors affecting the scale of the wind damage were: (1) the extensive mesocyclone which evolved to the mesoscale convective vortex (MCV), and (2) a strong rear flank downdraft interacting with the rear inflow jet (RIJ).