Numerical simulations of the Piedmont flood of 4-6 November 1994

A case study of the 1994 Piedmont flood is carried out by performing several numerical experiments using the MM5 model. We report on sensitivity tests and analyses that suggest the following description of the events leading to the flood: rising motion ahead of an upper-level trough, progressing from Spain towards Italy, initiated deep convection within the conditionally unstable air existing over the Mediterranean. Thus, a band of intense precipitation and low-level southerly winds formed and moved eastward with the upper trough. As the rain band and strong southerlies encountered the western Alps, moist air was lifted, resulting in large amounts of rainfall. The associated latent-heat-related upward motion produced a strong positive vorticity anomaly over the western Alps with associated low-level easterlies in the Po Valley which appear to have played a major role in retarding the generally eastward progress of the rain band over Piedmont.