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.