Impact of the SST and topography on the development of a large-hail storm event, on the Adriatic Sea

On July 10, 2019 an unusual and severe weather event hit Italy: a trough extending southward from northern Europe affected Italy and the Balkans, as it advected cold air over the Adriatic Sea, causing heavy damage because of giant hailstones reaching the ground. Between 08 UTC and 12 UTC of July 10, 2019, a deep convective cell developed along the coast of Marche in the vicinity of Ancona and quickly moved southward along the coast producing intense rainfall and hail, in particular near Pescara. In this work, the dynamics and thermodynamics responsible for triggering and maintaining the storm are investigated using the WRF (Weather Research and Forecasting) numerical model with the HAILCAST module activated. Several numerical experiments are carried out using a 1-km grid spacing with the aim of investigating in particular the impact of the orography and the SST anomaly in triggering and guiding the convective system. The results show that both the topography and the air-sea interaction played a key role: the topography guided the cold and dry air coming from the north, while the warm SST favored the instability of the environment. The SST anomaly plays a crucial role in creating the conditions necessary to generate the favorable conditions that led to the supercell and the giant hailstorm.