The presentation is based on the observations of the Spol radar to validate the fine scale Meso-NH simulations. The two days of the IOP2 (19-20 September 1999) are concerned by a strong prefrontal convection associated with multiple arrivals of moist low-levels zones impinging the coastal orographies (French Alps and Apennines). Some of these convective coastal episods propagated in the stationnary South-West upper-levels flow towards the Lago Maggiore target area(LMTA). The duration of the precipitation is very long and the hourly amounts are not very strong. An eastern low-levels flow localised in the north part of the Po valley(Fig1: Backward trajectories of low-level flow) is modulated by the barrier wind, the Thyrrenean sea entry, and the Adriatic sea entry. The intensification of the convection over the Monte Rosa eastern slopes is correlated with the intensity of this eastern low-level jet(Fig2: Rain around Mt Rosa and wind at the Spol location). The cape values keep rather homogeneous and weak inside the Po valley. The high cape values present over the Mediterranean sea and the Ligurian sea give intense convective events over Maritim Alps and Apennines. This last orography looks like a barrier for the maritim boundary layer and thus provides a protection from severe convection over LMTA.