Climatology of hail in the triple border Paraná, Santa Catarina (Brazil) and Argentina

Hailstorms cause great damage to plantations, kill animals and cause great damage to the population. The southern region of Brazil suffers from the damages caused by hailstorms each year, with the triple border of Paraná, Santa Catarina, and Argentina being the region with the highest incidence of this event. With averages above 2.60 days yr−1 recorded at Bernardo de Irigoyen, Argentina, Chapecó and São Miguel do Oeste stations in Santa Catarina. >70% of events are recorded in late winter and spring, with September and October being the months with the highest number of occurrences. The trend analysis of hail events for winter and spring was carried out, and it was observed that for most seasons, there were no statistically significant trends for the analyzed series, but the station Montes Caseros, in Argentina presented a positive and significant tendency. The Bernardo de Irigoyen and Curuzu Cuatia stations, also in Argentina, have shown a significant negative trend that may be the result of global warming. The synoptic analysis of three events suggests that there is a combined action of atmospheric systems, which in association with the topography of the region, promote the development of severe hailstorms. There is evidence that the combination of the atmospheric conditions, including South American Low-Level Jet (SALLJ), local thermodynamic instability, frontal systems, and strong upper-level winds, create a favorable environment for hail formation in deep convection. This combination involves the transport of heat and moisture from tropical regions, high level divergence and strong directional wind shear.