High-resolution numerical simulations of the convective system observed in the Lago Maggiore area on 17 September 1999 (MAP IOP 2a)

During Intensive Observing Period (IOP) 2a of the Mesoscale Alpine Programme (MAP) a significant convective system developed in the Lago Maggiore area. Its evolution is simulated using the Meso-NH model run over three nested domains with a 2 km horizontal resolution for the finest grid. Model results are assessed by comparing computed precipitation and model radar reflectivities with observed parameters. A control simulation initialized with European Centre for Medium-Range Weather Forecasts analyses and run with the standard microphysical scheme of the model yields fairly realistic results. Neglecting the ice processes in the microphysical scheme degrades the numerical results, whereas, significant improvement is obtained when heavy rimed particles are considered to be hail instead of graupel.