CATASTROPHIC RAINFALLS IN THE WEST MEDITERRANEAN AREA

Meteorological and thermodynamic factors associated with catastrophic flood events affecting the West Mediterranean Area have been studied. First of all, the usually assumed causal connection between cut-off lo ws aloft and severe storms has been thoroughly investigated. Once iden tified the general meteorological features, the synoptic- scale patter n and forcing are studied by using objective techniques. The thermodyn amic analysis took specific form in the study of stability, precipitab le water mass, convective available potential energy, vertical wind sh ear and bulk Richardson number. The combination of the synoptic and th ermodynamic results show a strong quasi-geostrophic forcing for vertic al motion at low levels while only a weak forcing at 500 hPa, high val ues of precipitable water mass produced by a strong convergence of wat er vapour near surface and convective and latent instability. Composit e charts delineating the area covered by each of the indicated factors seem to be an effective tool for delimiting the area where mesoscale focusing mechanisms become effective.