In Switzerland, the precipitation did not fall continuously between 30 April and 4 May but occurred in the affected region in three successive phases. The first phase started during the night of 30 April to 1 May, when the atmospheric river approached Switzerland from the west. The ascent of the moist air above the Swiss topography first caused precipitation over the Jura and at the foot of the Jura mountains, and then extended over the whole northern side of the Alps as the moist air travelled across Switzerland. The precipitation lasted until the morning of 2 May.
During most of the day of 2 May, the transport of moisture towards Switzerland was reduced, allowing a break in precipitation. In the afternoon, a new inflow of moist air from the atmospheric river arrived from the west-south-west, producing the second and third precipitation phases recorded in the affected region on 2 and 3 May. At the same time, a warm front passed over Switzerland, bringing warmer air from the south-west and causing a rise in temperatures.
On 4 May, the flow changed direction and switched from a westerly to a southerly flow, causing a situation of foehn and a further increase in temperatures on the northern side of the Alps, as well as a decrease in precipitation in that area.