Comparing Idealized Simulations of Supercell Thunderstorms in Current vs. "Business as Usual" Future Environments

Abstract:

Supercell thunderstorms occur most frequently in the Great Plains of the United States and are often responsible for extreme severe weather, including the majority of violent tornadoes and large hail. The impacts of anthropogenic climate change (ACC) on supercell thunderstorms, their environment, and therefore severe weather is the subject of much ongoing research. This study assesses how ACC’s impact on supercell environments cascades down to create storm scale changes in supercell behavior, characteristics, and severe weather production.

First, using a convective-allowing dynamically downscaled Weather Research and Forecasting (WRF) simulation of a modern and future climate under the RCP 8.5 scenario, supercell thunderstorms were identified and tracked through each 13 year integration. Regional three-dimensional grids of supercell-relative environments were collected each hour throughout each supercell’s lifetime, followed by analysis of the differences between the modern and future environments. The future environment showed the expected net increase in convective available potential energy (CAPE) and convective inhibition (CIN), while showing little change in the kinematic wind profiles. Increased CAPE and unchanged shear would indicate a net increase in supercell favorability; however, changes in CIN potentially limit this.

To better understand the actual impact of these conflicting factors on supercell morphology and severe weather, these WRF environments were then used as the input for an ensemble of fine-scale (250 m horizontal grid spacing) idealized simulations using the Cloud Model (CM1). These simulations allow for more accurate representation of internal dynamic supercell processes relative to the WRF simulations and also allow for direct depiction of the sensible impact of supercell-related severe weather. The ensemble of simulations will draw from the full range of storm-relative environments, including the mean inflow, high and low end inflow (e.g., 90th and 10th percentiles) thermodynamically favorable environments, and high and low end kinematic environments. The differences in the ensemble of modern and future-driven CM1 simulations will show the direct and indirect impacts that climate change causes and how severe weather risk will change in a future climate.