Impacts of Large Scale Natural Climate Variability on Severe Weather Over the United States

Previous studies have examined how future, projected changes in climate might impact the frequency and intensity of severe weather environments over the continental United States (CONUS) in both convection-permitting regional climate simulations and global climate or Earth system models. However, none of these previous studies have used an ensemble approach to examine the influence of natural climate variability on severe weather environments in a future climate. In this study, we use data from a new 11-member ensemble of climate simulations with version 2.0 of the Community Earth System Model and other CMIP-6 (Coupled Model Intercomparison Project) coupled models to examine severe weather environments using Convective Available Potential Energy (CAPE), Convective Inhibition (CIN), 0-6 km bulk vertical wind shear (S06), and the product of CAPE and wind shear (CAPES06). In addition to studying how the large-scale thermodynamic environment for severe convection may evolve in the future over the CONUS, we also analyze how it evolved over the historical record using CESM data through the 20th century. Moreover, by utilizing large-ensembles, changes in the thermodynamic environment due to unforced climate variability can also be examined, including changes due to variations in sea surface temperatures such as those associated with the Atlantic Multidecadal Oscillation and other leading patterns of natural climate variability. How low-frequency, unforced climate variability influences the thermodynamic environment critical for severe weather has not been examined extensively to date, even though it is likely a dominant influence regionally. Improved understanding of the causes of longer-timescale variability in severe weather, both natural and anthropogenic, will improve future predictions as well as enhance resilience to severe weather outbreaks.