Warning the public about hail: determining the potential for short-term damage mitigation

Previous attempts to mitigate hail damage have focused primarily on protective efforts, such as insurance programs, which require long-term planning. Very little research has been done to determine what actions can be taken to prevent hail damage just before it occurs. In this study, hail reports taken from the National Climatic Data Center (NCDC) Storm Events Database were compared with NWS warnings for Colorado, Massachusetts, Oklahoma, and South Carolina during the years of 1999-2008. Warning accuracy and average lead time were determined for all hail reports during 1999 and 2000 as well as damaging hail reports between 1999 and 2008. It was found that in general, under the county warning system, sufficient lead time existed for mitigating action by the public. While less than 50% of NWS Severe Thunderstorm Warnings resulted in hail reports, it is likely that many hail events were not reported in the NCDC data base. Using data from the Severe Hazards Analysis and Verification Experiment (SHAVE), an average hail swath size of 863 square kilometers (333.2 square miles) was calculated from 14 hail swaths across the United States. The average polygon warning size covered more area than the average hail swath size, while county warnings covered a much larger area and would prompt an unnecessary number of people to take mitigating action. There are serious limitations as to the data sources available to make decisions for damage mitigation. A more thorough and accurate data base would improve the economic cost-benefit analysis of various possible mitigation methods.