8.07 Verification of Radar-based Hail Detection Product

Large hail is regularly observed in Belgium and The Netherlands and is sometimes the cause of severe damage on e.g. crops, greenhouses, roofs and cars. Most severe hail events occur in summer and are associated with intense thunderstorms producing large hail stones. Hail is a very local phenomenon, in time and space, which can not be easily detected with ground observational networks. Due to its wide spatial coverage and relatively fine spatial and temporal resolution, weather radar appears as a valuable tool for the real-time detection of hail. In current operational networks most radars are single wavelength and single polarization radars and various methods have been proposed for detecting hail using reflectivity measurements from this type of radar. Most of these methods rely on the analysis of the vertical profiles of reflectivity. These profiles are extracted from three-dimensional data generated by a scan at multiple elevations. A hail detection algorithm mainly based on the 45-dBZ radar echotop is operationally used at the national weather services of Belgium (RMI) and The Netherlands (KNMI). The probability of hail estimated by the algorithm is affected by various sources of error and a careful verification of this product is required. In this paper we present two different verification methods. The first method is based on the verification of the results of the hail detection algorithm for a large number of hail events reported at ground.