Future Changes in Severe Thunderstorm Environments Over the United States: A Synoptic-Scale Approach

The global mean air temperature has been increasing in recent decades at an unprecedented rate, affecting weather climate patterns across the world. Following Clausius-Clapeyron scaling, tropospheric warming will very likely impact thermodynamic instability, and hence the likelihood of thunderstorms, including severe convective storms. While increasing low-level moisture and thermodynamic instability may favor the formation of severe thunderstorms, changes in vertical wind shear and convective inhibition may act as mitigating factors. Due to this complex interplay, future changes in severe thunderstorms and the perils associated with them remain largely uncertain. Studies focusing on severe weather proxies such as convective available potential energy and 0-6 km wind shear suggest that these component parameters exhibit large biases that vary from model to model. Therefore, in this study, we explore the 500 mb geopotential height fields (Z500) from global climate models (GCMs), which in the mean are relatively consistent across different models. Using self-organizing maps (SOMs), we identify the dominant synoptic-scale modes associated with severe thunderstorm occurrences over the United States from GCMs. We apply SOMs to Z500 fields from 12 models from the Coupled Model Intercomparison Project phase 6 (CMIP6) and ERA5 reanalysis for the historical period (1979-2014). Then we extend the analysis to the SSP585 scenario to investigate how the dominant synoptic-scale modes may change in future (2015-2100). Results suggest that variability across the CMIP6 ensemble in terms of synoptic processes is much larger than might be expected from prior studies, and as overshadowed by increases to thermodynamic favorability. The analysis will show how various clusters are likely to evolve and how these patterns differ geographically in a warmer climate. The results from this study will provide new insights that will provide novel insights into how severe convective storm environments change in our warming world.