For all precipitation accumulation durations, the Ticino stands out as an area affected by very heavy precipitation. At the other end of the scale, the largest amounts reached in the inner Alpine valleys are very modest, especially in the Rhone and the Inn valleys.
North of the Rhone and Rhine valleys, the spatial distribution of precipitation depends on the duration of accumulation. For durations exceeding a day, the northern Alpine rim (Prealps) and the Jura mountains experience heavier precipitation than the Plateau, thus highlighting topographical features. This pattern reflects the frequency of lightning strikes, and is consistent with the fact that thunderstorms are likely to contribute substantially to 1 day, but also to 5 day precipitation maxima.
At very short durations, on the other hand, the signature of the northern Alps is not visible: very heavy hourly or 10 minute precipitation does not depend on topography. (Note that this is not the case for average hourly or 10 minute precipitation, which displays the largest values over the northern Alpine rim and the Jura mountains, not shown). The reasons for this are unclear, but it is possible that while the generation of thunderstorms is more frequent along the northern Alpine rim than in the plain below, they are transported northwards or northeastwards by the large-scale flow and reach full maturity over the Plateau.
The following slide-show displays the percentage of years in which the yearly maxima falls in a given season (winter: December-January-February; spring: March-April-May; summer: June-July-August; autumn: September-October-November).