Synoptic patterns and mesoscale precursors of Italian tornadoes

Abstract

An analysis of synoptic patterns and mesoscale precursors is produced for Italian tornadoes for the period 2000–2018. Anomaly maps of different parameters are extracted from ERA-5 reanalysis. To highlight typical large-scale configurations, a clustering analysis is applied to define different regional clusters, representative of areas affected by a large number of tornadoes. The analysis shows that: a)Significant anomalies of synoptic variables and mesoscale precursors are generally present over and nearby the region where tornadoes occur, in particular for significant tornadoes (EF2+). b) Differences among clusters suggest that the environmental conditions favourable to tornado development differ between southern and northern Italian regions. In the Ionian region and Sicily, tornadoes occur when the northern end of a warm/moist tongue is advected toward an area of strong low-level shear. In the northern regions, high-shear cold air intrusions from continental Europe, combined with the high humidity content due to intense evaporation from the Mediterranean during summer, favour supercell triggering. c) tornadoes in southern regions are characterised by the highest anomaly values in wind shear, storm relative helicity and CAPE; d) significant SST positive anomalies are observed for southern tornadoes.