Long-term changes in thunderstorm environments over Europe and the United States

The recent release of the ECMWF ERA5 reanalysis presents a significant opportunity for severe thunderstorm climatology. The reanalysis has a vertical resolution of 137 model (sigma) levels on a time step of 1 hour at 0.25 degree horizontal spacing. Such resolution allow exploration of previously undiscovered aspects of trends in convective environments including superior characterization of convective inhibition, a quantify that is very sensitive to the number of levels in the lowest portions of the atmosphere (in ERA5, 28 levels are available in the lowest 2 km). In this study we use ERA5 to present climatological characteristics of ingredients for a deep moist convection over Europe and the United States with a main emphasis on a long-term trends over the last 40-years. Parcel parameters are computed using the native model data. Our results indicate that a long-term decrease in instability and stronger convective inhibition causes a decline in a frequency of severe thunderstorm environments over the southern United States. Conversely, a pronounced multidecadal rise in a low-level moisture creates increasingly better conditions for severe thunderstorms over southern, central and northern parts of Europe. Both continents display a negative tendencies in the fraction of situations with convective initiation, which indicates that even despite increasing instability thunderstorms are less likely to develop due to stronger convective inhibition. Results from this study may provide further understanding as to potential connections to a warmer world over both Europe and the United States, along with context for the processes driving shifts in the convective environments.