Rainfall prediction with a limited-area model during an intense storm over northern italy

Summary

Numerical experiments have been performed to simulate a severe storm in the Valtellina Valley, in the central part of Northern Italy, with a version of the limited-area model UB/NMC (University of Belgrade, U.S. National Meteorological Center model). This situation is characterized by strong and persistent rainfall over confined spatial areas in the Alpine region, where observations from synoptic and ENEL (National Electricity Board of Italy) stations revealed the intensity of the phenomenon. A first set of experiments was performed with ECMWF (European Centre for Medium Range Weather Forecasts) initialized analyses as initial and boundary conditions. These experiments were run with eta and sigma vertical-coordinate system, with different horizontal resolution and over two area domains. A second set of integrations with ECMWF operational forecasts as boundary conditions shows good agreement with observations, as is revealed by threat scores of the precipitation field. It is shown how the use of high horizontal resolution (0.25×0.25 degrees) enables the model to better resolve the spatial configuration of this situation. This work points out the capability of the ENEL version of the limited-area model UB/NMC to predict severe convective storms in mountain areas.