A 22-Year Hail Climatology using GridRad MESH Observations

Severe hail accounts for the vast majority of severe weather-induced property loss in the United States each year. Assessments of spatial and temporal hail fall characteristics using hail reports are plagued by serious limitations in report databases, including biases in reported sizes, time of occurrence, and location. To mitigate these issues, many studies have used observations from the Next Generation Weather Radar network (NEXRAD) or have used environmental hail proxies from reanalyses. While recent NEXRAD upgrades to dual-polarization capabilities provide improved hydrometeor discrimination, it is still beneficial to apply and improve upon single-polarization techniques for hail fall climatologies given the longer data record. Previous work has utilized the single-polarization parameter ‘‘maximum expected size of hail’’ (MESH) to analyze hail fall characteristics. In addition to previous work being limited in time, updated efforts are needed to include recent improvements that have been made to MESH.

This study aims to quantify hail fall characteristics during a 22-year period, a markedly longer timeframe than previous studies, using both radar observations and reanalyses. Environments likely to produce hail can be identified by leveraging reanalyses to better inform radar-derived hail proxies. First, the improved MESH configuration is applied to the full archive of gridded hourly radar observations known as GridRad (1995-2016). Next, environmental constraints obtained from the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) are applied to the MESH distributions to produce a modified hail fall climatology that accounts for the likelihood of hail reaching the ground based on melting characteristics. Spatial, diurnal, and seasonal patterns are investigated for each of these climatologies and evaluated against hail report distributions. Results show that in contrast to the report climatology indicating only one major hail frequency maximum centered on the Great Plains, the MESH-only method characterizes two regions, the Great Plains and the Gulf Coast. The inclusion of environmental information is found to correct some of these differences between MESH and observations, suggesting that MESH-only estimates of hail climatology need be treated carefully.