Future Changes in Hail Occurrence in the United States Determined through Convection-Permitting Dynamical Downscaling

The effect of anthropogenically enhanced greenhouse gas concentrations on the frequency and intensity of hail depends on a range of physical processes and scales. These include the environmental support of the hail-generating convective storms and the frequency of their initiation, the storm volume over which hail growth is promoted, and the depth of the lower atmosphere conducive to melting. Here, we use high-resolution (convection permitting) dynamical downscaling to simultaneously account for these effects. We find broad geographical areas of increases in the frequency of large hail (greater than or similar to 35-mm diameter) over the United States, during all four seasons. Increases in very large hail (greater than or similar to 50-mm diameter) are mostly confined to the central United States, during boreal spring and summer. And, although increases in moderate hail (greater than or similar to 20-mm diameter) are also found throughout the year, decreases occur over much of the eastern United States in summer. Such decreases result from a projected decrease in convective-storm frequency. Overall, these results suggest that the annual U.S. hail season may begin earlier in the year, be lengthened by more than a week, and exhibit more interannual variability in the future.