Improving Hail Diagnosis in Thunderstorms by Combining Radar and Lightning Detection Data

Recent studies indicate an increasing frequency of hailstorms in the Mediterranean region, strengthening the need for improved monitoring and detection methods due to their impacts on human safety and socio-economic activities. This study proposes a real-time method for hail diagnosis in thunderstorms based on the joint use of X-band weather radars and lightning measurements. The approach integrates the Vertically Integrated Liquid Density (VILD) algorithm with a new version of the lightning jump algorithm (hail lightning jump), relating hail growth mechanisms to VILD maxima and lightning-derived variables. Hail reports were used to classify hailstorm severity and link hail occurrence with radar and lightning variables. The 31 confirmed hailstorms examined in Southern Italy show comparable sensitivity of the radar- and lightning-based methods, which identify 80.6% and 77.4% of the events, respectively. When combined using a logical “OR” configuration, the fraction of identified hail events increases to 93.5%. Lightning-based analysis over the Italian Peninsula shows higher lightning activity for very large hail events (≥5 cm) than for large hail cases (2–5 cm). A strong positive correlation between maximum hail size and lightning activity was also found. These results highlight the benefits of a combined approach and the crucial role of lightning activity in diagnosing hail formation and size in thunderstorms.