Mesoscale meteorological features associated with heavy precipitation in the southern Alpine region

Several episodes of heavy precipitation, which occurred in the region south of the Alps, have been simulated by means of the mesoscale model BOLAM3. Each case was run at 3 different resolutions, up to 4km grid interval. The quantitative precipitation "forecast" fields are compared with available rain data. In general, satisfactory results are obtained in terms of spatial distribution and timing of precipitation, except in cases in which pre-frontal convection is dominant. The diagnostics of phenomena involved in orographic precipitation identify the different mesoscale atmospheric features associated with the interaction with topography, like the formation of low level jets, convergence zones, rainbands, and organized convective systems. These appear as "ingredients" common to all the cases considered and are shown to be sensitive to orographic forcing, as well as to the latent heat exchange processes.