Evaluating Multi-Radar, Multi-Sensor Products for Surface Hailfall Diagnosis

Abstract

The operational deployment of the multi-radar, multi-sensor (MRMS) system has made available new products to use for hail detection. MRMS products are provided on a spatial grid and can give information on hail size and the spatial extent and distribution of the hail fall. This information is important to a wide audience, including warning forecasters needing to focus on areas for warning verification and insurance users needing to verify a claim. Products are typically verified and evaluated using hail reports from Storm Data, which are reports collected by local National Weather Service Offices. The National Severe Storms Laboratory conducted a project to collect reports of hail, including reports of “no hail” near storms, at high spatial resolution. This project, the Severe Hazards Analysis and Verification Experiment (SHAVE), collected tens of thousands of hail reports over ten years of operations. Three-hundred eighty-nine SHAVE operations, which yielded 21 184 SHAVE reports and 2814 Storm Data reports, are investigated. Nine MRMS products were evaluated with the reflectivity at lowest altitude demonstrating the best discrimination for where hail of any size fell and the maximum expected size of hail product provided the best discrimination for severe-sized hail. SHAVE- and Storm Data-based evaluations showed marked differences in product skill scores. Discussions on the differences between the hail report databases and explorations of vertical profiles of reflectivity are included.