This study documents atmospheric conditions, development, and evolution of a severe weather outbreak that occurred on 11 August 2017 in Poland. The emphasis is on analyzing system morphology and highlighting the importance of a mesovortex in producing the most significant wind damages. A derecho-producing mesoscale convective system (MCS) had a remarkable intensity and was one of the most impactful convective storms in the history of Poland. It destroyed and partially damaged 79 700 ha of forest (9.8 million m3 of wood), 6 people lost their lives, and 58 were injured. The MCS developed in an environment of high 0–3-km wind shear (20–25 m s−1), strong 0–3-km storm relative helicity (200–600 m2 s−2), moderate most-unstable convective available potential energy (1000–2500 J kg−1), and high precipitable water (40–46 mm). Within the support of a midtropospheric jet, the MCS moved northeast with a simultaneous northeastward inflow of warm and very moist air, which contributed to strong downdrafts. A mesocyclone embedded in the convective line induced the rear inflow jet (RIJ) to descend and develop a bow echo. In the mature stage, a supercell evolved into a bookend vortex and later into a mesoscale convective vortex. Swaths of the most significant wind damage followed the aforementioned vortex features. A high-resolution simulation performed with initial conditions derived from GFS and ECMWF global models predicted the possibility of a linear MCS with widespread damaging wind gusts and embedded supercells. Simulations highlighted the importance of cloud cover in the preconvective environment, which influenced the placement and propagation of the resulting MCS.

The main objective of this research was to determine the synoptic and thermodynamic conditions accompanying the development of two severe thunderstorms that caused significant damage in Warsaw. The storm events of 17 June and 4 September 2016 were analysed. Materials used in the research included meteorological, aerological and radar data, as well as the Fire Service interventions database. These data allowed the conditions for the formation of the storms and their spatial variations in terms of intensity to be determined. It was shown that damage in Warsaw was caused by phenomena associated with supercell storms that developed in a moderate CAPE environment and a strong shear. It was confirmed that the geometry of the city increased the wind speed and modified its direction locally. In addition, it was found that the data on the number of Fire Service interventions clearly reflected the spatial variations in storm intensity by corresponding radar signatures to the high intensity of meteorological phenomena.

<p>Each year supercell storms in Europe are responsible for significant property damage and cause injury and death to people. Storms that have a deep persistent rotating updraft are capable of generating particularly violent phenomena - flash floods, large hail and strong wind gusts of convective origin. Supercells are also responsible for producing the strongest tornadoes with intensity of even F4-F5 in Fujita scale as evidenced over the recent decades across Europe, including Poland. Despite significant hazards posed by these types of storms, no research on climatological aspects of supercell thunderstorms in Poland has been carried out so far.</p> <p>The goal of this work was to study spatial and temporal characteristics of supercell thunderstorms in Poland between 2008 and 2022. In order to accomplish this task, a vector-tabular database of supercell thunderstorms over Poland was created, based on a manual analysis of 10-minute interval radar data accompanied by severe weather reports from the European Severe Weather Database (ESWD). The typical radar-derived signatures of supercells (e.g. bounded weak echo region, velocity couplet, hook echo) and/or long, continuous paths of high radar reflectivity with deviant motion were one of the main identification criterias. Identified supercells were classified into 3 groups, based on the confidence of their detection from plausible events to those producing significant severe weather. Manual evaluation of 15 years of radar and ESWD data allowed to analyze in the climatological context supercells track widths and lengths, storm duration, spatiotemporal frequency, accompanying hazards and characteristics such as right- or left-moving movement propagation. Moreover, ERA5 reanalysis was used to study accompanying atmospheric environments of identified supercells. An addition of lightning data from the PERUN network enabled also to evaluate non-supercell storm environments to show differences with supercells.</p>

Each year supercell storms in Europe are responsible for significant property damage and cause injury and death to people. Storms that have a deep persistent rotating updraft are capable of generating particularly violent phenomena - flash floods, large hail and strong wind gusts of convective origin.Supercells are also responsible for producing the strongest tornadoes with intensity of even F4-F5 in Fujita scale as evidenced over the recent decades across Europe, including Poland. Despite significant hazards posed by these types of storms, no research on climatological aspects of supercell thunderstorms in Poland has been carried out so far. The goal of this work was to study spatial and temporal characteristics of supercell thunderstorms in Poland between 2008 and 2022. In order to accomplish this task, a vector-tabular database of supercell thunderstorms over Poland was created, based on a manual analysis of 10-minute interval radar data accompanied by severe weather reports from the European Severe Weather Database (ESWD). The typical radar-derived signatures of supercells (e.g. bounded weak echo region, velocity couplet, hook echo) and/or long, continuous paths of high radar reflectivity with deviant motion were one of the main identification criteria. Identified supercells were classified into 3 groups, based on the confidence of their detection from plausible events to those producing significant severe weather. Manual evaluation of 15 years of radar and ESWD data allowed to analyse in the climatological context supercells track widths and lengths, storm duration, spatiotemporal frequency, accompanying hazards and characteristics such as right- or left-moving movement propagation. Moreover, ERA5 reanalysis was used to study accompanying atmospheric environments of identified supercells. An addition of lightning data from the PERUN network enabled also to evaluate non-supercell storm environments to show differences with supercells.