In the second part of November 2002, the synoptic situation over the Mediterranean was characterized by a sequence of perturbations entering the area from the North Atlantic. In particular, the persistence of an upper-level North-Atlantic trough between the 23th and 27th of the month, set the conditions for very heavy precipitation over North Italy with high ground impact over some areas and floods (i.e. Milan, Pordenone). The impact at ground was possibly amplified by the ground wet saturation for precipitations that occurred in the previous period. The evolution of the perturbation entering the Mediterranean basin on Nov. the 24th was very slow due to a steady North Africa high pressure blocking the central-east basin side.

The prefrontal humid and warm flow associated with the trough, invested North of Italy and the interaction with the orography induced precipitation across the whole region. The persistence of the precipitation for a long time, caused very high rain accumulation, especially in mountainous areas (Fig. 1) with peaks of day precipitation of 170 mm in Liguria on Nov. 24 over Northern Apennines region (NAP on Fig. 1), 130 mm in Northern Alps (NAL) on Nov. 25th and of about 320 mm over Eastern Alps (EAL) on Nov. 25. On November 26th a cut-off low pressure isolated over Sardinia (West Mediterranean), evolving south-eastward, and continued to feed Northern regions with wet-unstable flow which made the precipitation still persisting there. On the next days the low pressure became shallower and moved farther to South-East, while a second trough entered the western Europe on Nov. 28th, thus inducing wet, warm and unstable air-flow over the western basin and North Italy, again with associated precipitation. The total accumulation for the period (10 days of persisting rain) reached very high peaks with about 400 total mm in NAL, 470 mm in NAP, and more than 700 mm in EAL (Fig. 1).