Possible Relative Humidity Changes below the Melting Level in Future Climates over the Contiguous United States

A comprehensive understanding of historical and future trends in hailfall frequency and intensity throughout the United States is desirable when considering the substantial damage and property loss that is often a consequence of intense hailstorms. One of the unknown factors controlling this frequency and intensity in a warmer climate is not only how the height of the melting level may change, possibly allowing more depth for melting before hail reaches the ground, but also how changes in the relative humidity over this depth may be realized. Decreases in the relative humidity can slow melting of falling hail by evaporatively cooling the hailstone surface. We are conducting an assessment of changes in the environmental relative humidity below the melting level over the contiguous United States using CMIP5 model output, specifically that from the GFDL-CM3 model, the MIROC5 model, and the NCAR-CCSM4 model, all using the RCP8.5 scenario. Results will reflect any changes over summer month averages conducted from 1990-1999 and 2090-2099. Conclusions drawn from these differences can be used to assess any changes in hailfall size and intensity from high-resolution simulations of future hailstorms being conducted within our research group, as well as for future studies.