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

Abstract

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