The Piedmont flood of November 1994: a testbed of forecasting capabilities of the CNR-ISAC meteorological model suite

The celebration of the 25th anniversary of the Piedmont flood was organized by the University of Piemonte Orientale in Alessandria, a town that was severely affected in November 1994. It has been an opportunity to reexamine the meteorological event and assess the potential of CNR-ISAC models, after more than 20 years of development, to accurately simulate the heavy precipitation at different lead times. The predictability of this extreme event has been studied on a wide range of space and time scales, from subseasonal to convection resolving, using a variety of model setups and initial conditions. The subseasonal experiment produces a precipitation anomaly that, even if underestimated, indicates some predictability beyond the second forecast week. At shorter ranges, results indicate that there is a consistent improvement in the precipitation forecast going from low-resolution hydrostatic to high-resolution nonhydrostatic models. It is only at very high resolution (500 m) that the convective activity extending to the north of the divide line of the Ligurian Apennines, which was responsible for the flood of the Tanaro River, is predicted with an intensity comparable with rain gauge observations. The main mesoscale phenomena that played a role in the different phases of the event have been also identified.