A multi-sensor and modeling analysis of a severe convective storm in Lake Maggiore area (northwestern Italy)

Abstract The analysis of a severe convective storm occurred in northwestern Italy during late summer 2012 is presented here. The event was characterized by heavy precipitation, hail and intense wind gusts, causing injuries and damages to trees, buildings and infrastructures. The description of the case study draws upon a wide palette of observational data. Surface and upper-air observations helped characterize the event, emphasizing the rapid changes in the meteorological parameters in the study area; satellite data highlights the presence of deep moist convection, associated with strong updrafts; Doppler radar allows the identification of the main features of the event in terms of storm-motion, hail detection/probability and the possible presence of a mesocyclone. A high-resolution (3 km inner grid spacing) simulation with the WRF (Weather Research and Forecasting) model was performed to study the atmospheric conditions conducive to convection, as well as to estimate the main instability parameters. The main features of the storm were well reproduced with WRF; furthermore, the high values of the simulated instability parameters denote the presence of favourable conditions for severe convection. The analysis of this event shows that supercells can develop also in a pre-alpine environment, characterized by a complex orography, in particular in the sub-regions where the local morphology creates conditions favourable for severe weather development.