Quasi-linear convective systems and derechos across Europe: ERA5 convective environments and synoptic-scale patterns

Each year, an average of 184 quasi-linear convective systems (QLCSs), including 6 derechos, occur across different parts of Europe, posing a significant societal impact. In this work, we analyze synoptic patterns and convective environments associated with QLCSs, considering their intensity and spatiotemporal variability. For this analysis, we used the QLCS database with 1469 manually identified cases based on the OPERA radar data, over a period of 8 years (2014–2021). For each case, we have chosen a representative ERA5 vertical profile representing the pre-convective environment ahead of the QLCS. In the performed analysis of synoptic-scale patterns, we found that warm-season cases develop primarily under large atmospheric instability setups, whereas during the cold part of the year, large-scale lift with marginal (but non-zero) CAPE and high vertical wind shear is the most common trigger. The mean vertical profiles presented in this work indicate the dominance of westerly and southwesterly flow, accompanied by steep mid-level lapse rates and small relative humidity over this layer. Except for warm-season QLCSs over the West and cold-season cases in Central Europe, QLCSs are associated with clockwise-curved mean hodographs. Analysis of convective parameters indicates that the intensity of warm-season QLCSs is well represented by downdraft-related metrics. Marginal and stronger QLCSs, including derechos, can be distinguished using atmospheric instability (CAPE), especially across Central Europe. Upper-level bulk wind shear was found to discriminate well between the severity of QLCSs in the cold season.