The climatology of supercell thunderstorms across Poland based on multisource data.

Supercell storms annually cause substantial property damage, injuries, and fatalities across Europe. These storms, characterized by deep, rotating updrafts, generate violent phenomena like flash floods, large hail, and strong convective winds. They are also responsible for Europe's most intense tornadoes (IF2+), including those in Poland. Despite these significant threats, there's been no prior climatological research on supercells in Poland.This study aimed to analyse the spatial and temporal characteristics of supercell thunderstorms in Poland over a 15-year period (2008-2022). To achieve this, a database of supercell thunderstorms has been developed. This involved manually analysing 10-minute interval radar data and severe weather reports from the European Severe Weather Database (ESWD). We also incorporated lightning data from the PERUN network to differentiate supercell environments from non-supercell storms. Identification criteria included typical radar signatures (e.g., bounded weak echo regions, velocity couplets, hook echoes) and/or long, continuous paths of high radar reflectivity with deviant motion. We categorized identified supercells into three groups based on detection confidence, ranging from plausible to those producing significant severe weather.Our analysis identified a total of 1748 confirmed and possible supercell cases, more than 100 as average per year. Nearly half of them (862 cases, 49.4%) were fully confirmed, with 616 (35.2%) highly probable and 270 (15.4%) possible, because of not enough sufficient data for full confirmation.This manual evaluation of 15 years of data allowed for a climatological analysis of supercell track widths and lengths, storm duration, spatiotemporal frequency, associated hazards, and propagation characteristics (e.g., right- or left-moving). The supercell season in Poland mirrors the general storm season, with most occurrences from May to August. The earliest detection was in early March, the latest in late October. Most cases were observed in southern Poland - an area with complex topography that may influence wind shear. Furthermore, we utilized ERA5 reanalysis to study the atmospheric environments accompanying these supercells, calculating pre-convective profiles and hodographs for each. A significant contribution of this work is the calculation of environmental parameters (like storm relative helicity or streamvise vorticity) using radar-derived observed storm motion vectors, rather than relying on estimations.