A mesoscale severe storm at Genoa: Considerations in reference to the prediction problem

An extreme event, which caused the absolute maximum in the yearly peak discharge time series of the Dora Baltea River (Aosta Valley) for the period 1925-1995 together with the absolute maximum of hourly rainfall at Genoa, is analysed. The storm affected the Italian regions of Liguria and northwestern Piedmont in September 1993. Synoptic scale "forcing", orographic effect, above normal sea surface temperatures and convection are considered as main meteorological factors contributing to the hydrogeological "disaster". On the basis of the examined case, nature and "scale" of the various factors involved are discussed, including the possible feedbacks of convection (either dynamic or thermodynamic). Finally some considerations about the development of a warning system for these extreme events are presented.