A significant tornado event near a dryline bulge in Northern Italy

A multi-scale observational analysis of a 1.6 km wide IF3 tornado in Northern Italy is conducted using radar and sounding data, ground weather stations, and damage surveys. The tornado occurred close to Alfonsine, along the Adriatic coast, on July 22, 2023, in one of the most tornado-prone regions of Europe. An initially hail-bearing supercell (which produced hailstones up to 10 cm in diameter) became tornadic as it approached a dryline bulge. During the transition from a hail-dominant to tornadic storm, the long-lived supercell generated a damaging Rear-Flank Downdraft (RFD) surge, with unusually cold wind gusts reaching 40 m/s. A dry and hot air mass from the southwest was partially ingested by the mesocyclone just before the tornadogenesis occurrence. At the same moment, the storm was also ingesting from the east a maritime air mass with very high values of equivalent potential temperature. A seamless wind damage pattern, transitioning from damage caused by straight-line wind gusts to tornadic damage, suggests that the tornado may have developed from the stretching of small-scale pre-tornadic vertical vorticity maxima within the RFD. As in other case of significant tornadoes in Northern Italy, the environment was characterized by strong deep layer shear and conditional instability, but weak low-level wind shear. However, numerical simulations indicate that along the dryline the low-level storm relative helicity and vertical vorticity were stronger, suggesting a higher tornado potential. The tornado resulted in only 14 injuries, likely because it impacted a sparsely populated area. Considering that past significant tornadoes in the region affected much more densely populated areas, and since no tornado warnings or shelters are currently in place, there are growing concerns about the potential catastrophic consequences of a future significant tornado in the highly populated areas of northeastern Italy.