Derecho Evolving from a Mesocyclone—A Study of 11 August 2017 Severe Weather Outbreak in Poland: Event Analysis and High-Resolution Simulation

Abstract

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.

Synoptic-scale conditions and convection-resolving hindcast experiments of a cold-season derecho on 3 January 2014 in western Europe

“…The CCLM is able to resolve deep moist convection (convection-resolving model; Baldauf et al, 2011;Prein et al, 2015) at grid spacing smaller than 4 km, while shallow convection is still parameterised. Thus, for the first nesting steps (D0, D1) the convective mass flux is parameterised after Tiedtke (1989), while for the higher-resolution runs (D2, D3) this scheme is only applied to shallow convection (see Table 1). As an upper boundary condition, damping against boundary fields is applied.…”

VDRAS and Polarimetric Radar Investigation of a Bow Echo Formation After a Squall Line Merged With a Preline Convective Cell

“…As the enhanced RIJ descended to the ground under the influence of heavy precipitation which produced an intensified downdraft, damaging winds (>40 m s −1 ) were produced near the surface consequently. Recently, Taszarek et al (2019) investigated a severe weather event in Poland, to find that the interaction of a convective line and a supercell resulted in a strengthened RIJ associated with a bow echo and the subsequent damaging surface winds.…”

Case study of a derecho wind storm on August 11-12, 2017 in Poland: part one

“…The whole storm covered a vast area about 540 km from Wrocław, through Poznan, Bydgoszcz, along Gdynia and Gdansk and part of the coast. Late in the evening of August 11, 2017, and at night from August 11/12, 2017, a squall line crossed the area from Wielkopolskie through Kujawsko-Pomorskie to Eastern Pomorskie (see Fig.1) [1,2]. This thunderstorm front moved very fast with high speed wind on August 11, 2017 at 18:00, it reached the borders of the Wielkopolskie province.…”

“…The thunderstorm caused much fear and despair for residents in its path. Based on the data collected in the European Severe Weather Database (ESWD) [1] and by authors of the paper [2], it appears that the storm meets the derecho criteria. The derecho wind storm criteria are as follows: a) The wind storm damage path must be at least 460 km long, b) Wind speed greater than or equal to 26 m/s (94 km/h) in three places on the path of damage, at least separated from each other of 74 km.…”

“…, 0 (2019) https://doi.org/10.1051/matecconf /201928 MATEC Web of Conferences 284 4 ICSF 2019 08001 0 80 1 g) the area of losses in valuable natural areas amounted to approximately 541 km 2 .…”