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Abstract This case study analyzes the 17 May 2019 cyclic, tornadic supercell from southwest Nebraska observed by the Targeted Observation by Radars and UAS of Supercells (TORUS) field experiment. Specifically, 12 multi-Doppler wind syntheses are generated over a 96-min period from 2301 UTC 17 May to 0037 UTC 18 May using two P-3 airborne radars and the ground-based NOXP research radar. Synthesized winds and reflectivity are assimilated into a diabatic Lagrangian analysis for the retrieval of thermodynamic data. The 4D wind fields are found to correlate well with observed tornadic and nontornadic periods, and several storm-scale features related to low-level mesocyclone (LLM) and near-ground rotation processes are documented. This includes vortex line arches that are a defining feature during the first EF2 tornado, followed by an occlusion process and reorganization period. During the most active tornadic period, backward trajectories reveal both inflow parcels and forward-flank parcels participate in the core of the 0–1-km rotation. While tilting of streamwise vorticity into vertical vorticity and subsequent powerful vertical stretching occurs for both inflow and forward-flank parcels, the solenoidal generation of streamwise vorticity is dominant with the latter. This resembles streamwise vorticity currents found within numerical simulations. Last, an intense left-flank convergence boundary develops coincident with the intensification of storm-relative inflow winds, with its formation and dissipation correlated with the final tornado. The 96-min analysis period with 4D kinematic and thermodynamic data makes this study one of the most detailed supercell case studies presented in the literature. Significance StatementA detailed analysis of a supercell that produced nine tornadoes within a 96-min period is presented. The supercell was observed by five radars, which are used to obtain information about the 3D wind, temperature, and moisture fields. Although computer simulations can provide detailed looks into supercell processes, collecting and analyzing observed supercell data of this quality is challenging and rare. We identify features within the supercell that are correlated with periods of strong and weak tornado production. Additionally, we identify the source region of air that is associated with low-level rotation in the supercell and comment on the importance of temperature gradients observed within the supercell, comparing these results to what has been found in simulations. 

Abstract Quasi-linear convective systems (QLCSs) are responsible for approximately a quarter of all tornado events in the U.S., but no field campaigns have focused specifically on collecting data to understand QLCS tornadogenesis. The Propagation, Evolution, and Rotation in Linear System (PERiLS) project was the first observational study of tornadoes associated with QLCSs ever undertaken. Participants were drawn from more than 10 universities, laboratories, and institutes, with over 100 students participating in field activities. The PERiLS field phases spanned two years, late winters and early springs of 2022 and 2023, to increase the probability of intercepting significant tornadic QLCS events in a range of large-scale and local environments. The field phases of PERiLS collected data in nine tornadic and nontornadic QLCSs with unprecedented detail and diversity of measurements. The design and execution of the PERiLS field phase and preliminary data and ongoing analyses are shown. 

Abstract Some supercellular tornado outbreaks are composed almost entirely of tornadic supercells, while most consist of both tornadic and nontornadic supercells sometimes in close proximity to each other. These differences are related to a balance between larger-scale environmental influences on storm development as well as more chaotic, internal evolution. For example, some environments may be potent enough to support tornadic supercells even if less predictable intrastorm characteristics are suboptimal for tornadogenesis, while less potent environments are supportive of tornadic supercells given optimal intrastorm characteristics. This study addresses the sensitivity of tornadogenesis to both environmental characteristics and storm-scale features using a cloud modeling approach. Two high-resolution ensembles of simulated supercells are produced in the near- and far-field environments observed in the inflow of tornadic supercells during the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2). All simulated supercells evolving in the near-field environment produce a tornado, and 33% of supercells evolving in the far-field environment produce a tornado. Composite differences between the two ensembles are shown to address storm-scale characteristics and processes impacting the volatility of tornadogenesis. Storm-scale variability in the ensembles is illustrated using empirical orthogonal function analysis, revealing storm-generated boundaries that may be linked to the volatility of tornadogenesis. Updrafts in the near-field ensemble are markedly stronger than those in the far-field ensemble during the time period in which the ensembles most differ in terms of tornado production. These results suggest that storm-environment modifications can influence the volatility of supercellular tornadogenesis. 

Abstract On 28 May 2019, a tornadic supercell, observed as part of Targeted Observation by UAS and Radars of Supercells (TORUS) produced an EF-2 tornado near Tipton, Kansas. The supercell was observed to interact with multiple preexisting airmass boundaries. These boundaries and attendant air masses were examined using unoccupied aircraft system (UAS), mobile mesonets, radiosondes, and dual-Doppler analyses derived from TORUS mobile radars. The cool-side air mass of one of these boundaries was found to have higher equivalent potential temperature and backed winds relative to the warm-side air mass; features associated with mesoscale air masses with high theta-e (MAHTEs). It is hypothesized that these characteristics may have facilitated tornadogenesis. The two additional boundaries were produced by a nearby supercell and appeared to weaken the tornadic supercell. This work represents the first time that UAS have been used to examine the impact of preexisting airmass boundaries on a supercell, and it provides insights into the influence environmental heterogeneities can have on the evolution of a supercell.