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

Forecasts struggle to predict the evolution of supercell thunderstorms during and after the evening transition due to an incomplete understanding of how they evolve in response to associated environmental changes. As the low-level environment cools and stabilizes, supercells can dissipate, merge with other convection, grow upscale, or be sustained as either a surface-based or elevated supercell. To better understand the connection between storm evolution and changes in the evening environment, 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 soundings between 0000 - 0500 UTC. Using these soundings, numerous thermodynamic and kinematic parameters are derived, including surface-based and most unstable CAPE and CIN, and low-level and deep-layer shear and storm-relative helicity. Trends in each parameter are identified and compared to storm evolution. Statistical tests are used to identify significant trends and differences among the supercell categories. The goal of this study is to better predict how supercells will evolve during the evening transition and which trends in environmental parameters can increase skill in forecasting.