Supercell Thunderstorm Updraft Accelerations During the Evening Transition

Abstract

The evolution of supercell thunderstorm environments during the evening transition provides mechanisms that would seemingly offer competing contributions to updraft accelerations: low-level cooling and associated stabilization detrimental to buoyancy accelerations and a low-level jet favorable to dynamic accelerations. To determine the impacts of changes to the thermodynamic and kinematic profiles on updraft accelerations during the evening transition, a suite of idealized simulations is initialized with unique combinations of thermodynamic and kinematic profiles representative of various stages of the evening transition. The core updraft is defined at each height for each simulation, and profiles of average acceleration terms within the updraft core are compared amongst simulations. It was found that the relative contributions of dynamic accelerations increased early in the evening transition but were not sustained. The thermodynamic evolution of the evening transition weakens low-level net updraft accelerations. The kinematic profile evolution increases low-level net updraft accelerations early in the evening transition, but those gains are lost later in the evening transition. Near-ground vertical vorticity stretching, an important mechanism in tornadogenesis, is most favored by the mid-transition kinematic profile.