Shape of hail and its thermodynamic characteristics related to records in Catalonia

Staring at a hailstone helps to determine various characteristics, such as shape or size. However, from the physics point of view, one of the most important characteristic is the type of growth. Each of the stone’ elements (nucleus, lobes, rings) is conductive to explaining the environmental behaviour of its formation and development stages. The thermodynamic variables derived from the upper-air soundings or the numerical weather prediction simulations can help us understand the differences between the different growth modes. In this way, the hail type has been analyzed according to its shape and size. The study has comprised 151 hailstorms that occurred in Catalonia (NE of the Iberian Peninsula) between 2017 and 2020. We have characterized the events according to different properties. The size of the stones (small, large and, huge), the shape (embryo, spherical, and irregular), and, the season of occurrence (spring, summer, and autumn) are the selected characterizing elements. Maximum vertical updraft velocity, vertical wind shear, and precipitable water content are the variables that explain better the behaviour of each category.