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Abstract.This study investigates, with the aid of a water vapor back-trajectory technique, the large-scale source

Severe and organized thunderstorms are historically responsible for high‐impact hydrometeorological events in the western Mediterranean area (Spain, France and Italy). This study presents a meteorological indices‐based forecasting tool developed by the Meteo‐Hydrological Functional Center of Civil Protection of Liguria Region for the prediction of these phenomena. The tool, in the form of a checklist, takes into account all the physical processes and thermodynamic ingredients driving the formation and the spatio‐temporal evolution of thunderstorms and their level of organization. The study was carried out on a series of events occurring in 2009–2014 to assess the checklist performance and identify the most relevant parameters and variables from a predictive ability standpoint. Some indices were found to be useful for general thunderstorm recognition but not necessarily for thunderstorms impacting most from a socio‐economic standpoint, namely strong and organized ones; other parameters exhibited a higher degree of reliability for the identification of severe and organized phenomena in Liguria. Furthermore, the analysis was useful for the identification of a seasonal dependence for many variables, for the recalibration of some thresholds in a new version of the checklist and for the identification of local patterns of low level winds favourable to the development and maintenance of well organized and stationary convective systems. The assessment of the new checklist for all the events in 2009–2014 showed a significant enhancement of the performance and helped to identify and sort out the role of each parameter better.

Downbursts are very disruptive weather events that can produce large amounts of damage. The most studied downbursts are those occurring in the United States and continental Europe, but they can happen globally. This work is an observational and modelling analysis of a major downburst event that occurred on 14 October 2016 over eastern Liguria (Italy). This downburst affected an area 30 km long and 10 km wide, producing observed wind gusts of 40 m/s with major impacts to railways, trees, and houses, with more than 2.5 million euros of damage. First, the general environment influencing this downburst is identified and analyzed, then the event is reproduced with a small multi-physics high-resolution ensemble using the Weather Research and Forecasting (WRF)–advanced research WRF (ARW) model, with 1 km horizontal grid spacing. The event was poorly predicted beforehand, and the difficulty in forecasting this event is confirmed by the fact that so few ensemble members suggested the occurrence of damaging winds over eastern Liguria. However, one of the eight members performed well and its output helped to reveal the primary mechanisms for the downburst, suggesting that high-resolution ensembles using mixed physics may be a useful tool for improving the prediction of similar extreme events in the Mediterranean region in the future.