THE VAISON-LA-ROMAINE FLASH-FLOOD - MESOSCALE ANALYSIS AND PREDICTABILITY ISSUES

On the morning and early afternoon of 22 September 1992, a flash flood (220 mm of rain in 3 h) occurred in the city of Vaison-La-Romaine, lo cated in southeastern France, causing numerous casualties and consider able property damage. It was generated by a combination of several mes oscale convective systems ahead of a slow-moving cord front associated with a cutoff low. The large-scale setting and a mesoscale analysis o f the case, together with estimates of radar-derived rain accumulation s, are presented. The mesoscale analysis demonstrates the complexity o f the case, which involved five precipitation systems. Orographic infl uences generated a cold pool and focused convective cell development i n a confined area, enabling two precipitation systems to be quasistati onary. Precipitation forecasts by different versions of two models (a fine mesh version of an operational limited area model, and an operati onal stretched global model) are summarized. They demonstrate the exte nt to which realistic rainfall forecasts may be produced for extreme m eteorological events such as this. One model exhibits a rather precise and realistic distribution and evolution of the precipitation pattern s, while all show significant accumulations. Finally, some of the obje ctive pieces of information useful for nowcasting rainfall location an d duration for such an event are discussed.