Observational analysis and simulations of a severe hailstorm in northeastern Italy

Hailstorms are relatively frequent in the Friuli Venezia Giulia region, northeastern Italy and, for that reason, a network of manual hailpads has been set up there since the late 1980s. On July 4, 2007, a record number of hailpads in the network were impacted by hail (115 out of about 360 total stations). To the best of the authors' knowledge, no other single hailstorm case-study has information coming from such a large number of hailpads impacted by hail. These hailpads are analysed using automatic software, able to interpret each hail dent as an ellipse. From these data, the distribution of hailstone diameters, areal hailstone density on the pads and total kinetic energy flux are computed and analysed in the present study. A parallel analysis of radar maximum reflectivity and cloud-to-ground lightning shows that the evolution of the hailstorm can be divided into three different phases, the first being the most severe in terms of lightning and hail. Finally, numerical simulations performed with a non-hydrostatic mesoscale model, implementing a prognostic module for the explicit simulation of hail (WRF-HAILCAST), show that the simulation system provides useful information on the severity of the event in terms of maximum hailstone diameter and reflectivity shape.