Hail Sizing: A Comparison of On-Site Data with Weather Data

When investigating buildings for potential hail damage, determination of the approximate hail size is an important part of the investigation. Weather data resources, including free data made available by the government and fee-based reports from third-party weather analysis services, are often used to help evaluate the reported or estimated hail size in the vicinity of a given site location. In addition, data collected during a site investigation provides valuable, site-specific information regarding hail occurrence(s) at a site. The authors have investigated buildings, and especially roof coverings, for damages from numerous hail events. Based on this experience and published studies regarding damage profiles from varying hail sizes, observations and measurements obtained during an investigation for hail damage are utilized to determine an estimate of hail size at a given site. The purpose of this paper is to discuss the methodology used for on-site evaluation of hail size and to compare estimated maximum hail sizes determined from these on-site investigations with the available weather data. Data from multiple storm events affecting populated areas, which generally provides for a more comprehensive and more closely-spaced set of data, will be used. The comparison of on-site evidence with the available weather data will show that this weather data can provide information of varying accuracy with regard to the sizing of hail, and that the data collected during an on-site investigation is essential for the accurate determination of the approximate hail size which has occurred at a given site.