The Impact of the Nocturnal Transition on the Lifetime and Evolution of Supercell Thunderstorms in the Great Plains

Abstract

AbstractPredicting the evolution of supercell thunderstorms during and after the evening transition is a known challenge due to an incomplete understanding of how these events evolve in response to associated environmental changes. To quantify the connection between storm evolution and environmental changes during the nocturnal transition, 157 initially isolated Great Plains supercell thunderstorms occurring between 2005 and 2016 are examined. Each supercell is categorized as either maintained, dissipating, growing upscale, or merging. Changes in the inflow environment are quantified using hourly RUC and RAP model proximity soundings between 1 h prior to local sunset time and 5 h postsunset. Using these soundings, numerous thermodynamic and kinematic parameters are derived, and distributions of these parameter values are statistically compared among the evolution categories. It was found that each evolution classification existed in a unique set of kinematic and thermodynamic parameters; this distinction was most evident when comparing maintained and dissipation categories. In particular, storm-relative helicity, most unstable convective inhibition (MUCIN), and associated composite parameters were best able to distinguish supercell evolution. Notably, maintained supercells were characterized by significant increases in storm-relative helicity and comparatively smaller increases in the magnitude of MUCIN during the nocturnal transition; together, these parameters promote a sustained and robust rotating updraft. A convective inhibition?scaled supercell composite parameter is proposed to further assist in predicting supercell maintenance during the nocturnal transition.