User‐Tailored Impact‐Based Hail Forecasts in Switzerland

ABSTRACT Hail represents a major atmospheric peril in terms of monetary damages in many European countries. This highlights the potential benefit of hail‐damage predictions, so‐called impact‐based hail forecasts, that can trigger preventive actions. The construction of impact‐based forecasts is often complicated by a lack of data, especially with respect to impacts or damages. In this work, we implement and evaluate two types of impact‐based hail forecasts and impact‐oriented hail warnings that are tailored for specific user groups, using a uniquely comprehensive dataset comprising operational weather forecasts from the Swiss meteorological office and hail damage records provided by cantonal building insurance agencies in Switzerland. We first analyze impact‐oriented hail warnings that are directed toward the general population. Although these warnings are based on meteorological thresholds (hail size), they are termed impact‐oriented because the thresholds are chosen to represent the vulnerability of exposed assets. Second, we implement and evaluate impact‐based forecasts that incorporate a complete impact model—including meteorological hazard, the (spatial) distribution of exposed assets, and their vulnerability—that can be of value to larger institutions and companies. Our study highlights how impact‐based forecasts can be tailored to specific user groups, and how the availability of high‐resolution data enables adjusting impact forecasts for optimal use. Given the limited predictability of hail as a thunderstorm‐related phenomenon, the skill of impact forecasts remains below commonly accepted benchmarks for operational use warning products issued by authoritative warning agencies. Nonetheless, we argue that, in certain contexts, these products can still offer value despite their limited skill.