Spatial and temporal variability of hail falls and estimation of maximum diameter from meteorological variables

Abstract

Abstract When studying hail falls, it is common to mention their variability, but not so much to present results in support of this statement and do so in detail. This is because of the difficulty of accurately understanding hail falls in spatial and temporal terms. It is even more difficult to ascertain the characteristics of hailstones precipitated by storms. In this paper, we use hailpad databases, which are known to give detailed information on hail falls, to determine spatial and temporal variability across two networks in the Middle Ebro Valley (Northeast Spain), just a few tens kilometers apart. These results demonstrate the importance of having sound ground-based information obtained directly. The databases used have 2865 hailpads that measured 197,076 hailstone impacts (≥ 5\xa0mm). When classifying the severity of storms, the maximum hail diameter is typically used. Among all days with hail events, we selected 71 hailstorms that were tracked over their entire duration, having formed and dissipated within either of the two hailpad networks. We present a methodology and application to determine a mathematical equation that expresses the maximum diameter as a function of meteorological variables, analyzing possible uncertainties to make short-term predictions. This equation facilitates improvement of our knowledge of factors that influence the appearance of storms and the classification of predicted severity.