THE EPISODE OF THUNDERSTORM OUTBREAK OF 10 JUNE 1990 OVER NORTHERN ITALY

We examine a case of organized thunderstorm development over the Po Valley of Northern Italy that occurred in June 1990, during the MATREP field experiment. The development of the convective activity is studied in the perspective of the synoptic and mesoscale situation, which was characterized by the moviment of a cold mid-tropospheric vortex over the region, associated with a very low tropopause and an isolated maximum of potential vorticity in the upper troposphere. This situation is contrasted with a case considered in a previous paper (A. BUZZI and P. P. ALBERONI: Meteorol. Atmos. Phys., 48, 205 (1992)), in which the propagation of a cold front into the Po Valley, associated with a lee cyclone, constituted the main dynamical forcing for the organized convection. The mesoscale analyses are carried out using the dense surface network, with the aid of semiquantitative information provided by the satellite and radar images. The mesoscale analyses allow a detailed definition of the pre-convective environment and reveal the thunderstorm-related perturbations of the low-level temperature and wind fields. A high degree of consistency is found between the surface wind analyses and the radar echoes, revealing the position and structure of the gust fronts.