Although extended only two degrees in lat. Switzerland shows, given the variety of the relief, a great diversity of climates. Altogether it belongs to the transition area between the countries with an Atlantic climate of central-western Europe and those with a continental climate of Eastern Europe: from the Atlantic comes the winds from the West and from the NW, mild and bringing abundant rainfall; from E. and NE., on the other hand, cold and dry continental winds. On the southern side of the Alps (Canton Ticino) the Mediterranean influence is felt.
For the general characteristics of the Alpine area, see. Alps: Climate; but some peculiarities that take on particular prominence in the Swiss part of the Alps must be pointed out here. In the first place, as regards the wind regime, the great importance that the föhn assumes in the valleys of the external side (v.). It manifests itself as a violent downward current, hot and dry, especially in the valleys that open on the external slope with SE.-NO direction. or China-N. (Rhine valley to Lake Constance, Linth, Reuss, Rhone valleys, from Martigny to Lake Geneva) making its influence felt up to the Plateau region and the Jura; it blows especially in the months of March, April and May, but also in October and November. If the föhn sometimes causes serious damage, it does however have a beneficial influence on these regions, which in terms of heat can be considered as climatic oases. In general, as regards the temperature, local differences can be noted in the Alpine region, even very strong due to the different position and the presence of the major transversal and longitudinal furrows that determine climatic conditions in the heart of the mountain in stark contrast to those of the nearby slopes. As in all the Alps, the phenomenon of temperature inversion frequently occurs during the winter.
The geographical distribution of rainfall varies greatly according to local conditions (see map). They are abundant in all the NE Alps and Prealps. between Reuss and Rhine, much less in the central and western Alpine area, somewhat sheltered from the humid winds of the Atlantic by the Jura, but the highest massifs of the Bernese and Pennine Alps receive copious rainfall. A little less rain is the alpine area of Grisons. The Rhône-Rhine longitudinal furrow represents an area of scarce rainfall, especially in the Valais, where the lowest values in Switzerland are reached: the flat bottom of the great glacial furrow receives less than 600 mm. annual rainfall, while the winter temperatures are relatively very mild, so much so that vines can thrive on the side facing China
In all the Alps, precipitation occurs largely in the form of snow: the limit of eternal snow is lower the greater the annual amount of precipitation, therefore it drops to 2450 m. in the Säntis Mountain, while it rises to 2800–2900 in the Bernese Oberland, to 3000-3200 in the Valais.
The climate of the Canton of Ticino is much milder than that of the northern side of the Alps. Its valleys are beaten by downward winds that blow from N. especially in winter and spring, which have characteristics similar to that of the föhn. A true climatic oasis are the shores of Lake Maggiore and Iago di Lugano on which Mediterranean plants thrive. The precipitations, which mark a maximum in autumn and another secondary in spring-summer, are abundant, but are concentrated in fewer rainy days than in the northern slope, and preferably fall in the form of violent downpours; fogs are also much less frequent.
Compared to the Alps taken as a whole and the Jura, the plateau has a relatively mild climate. It is beaten by the mild and humid winds from the Atlantic, but also by the cold and dry winds of the North and NE. (locally bise) which blow violently especially when channeled into the western and southwestern part of the region. Temperatures there are relatively mild, especially towards the east: the region is largely between the January average isotherms of 0 ° and −2 ° (similar temperatures are found only in the Rhone valley, or in the Canton of Ticino), while also summer temperatures are not excessive. Fogs are frequent in autumn and winter. Precipitation decreases from the edge of the Alps towards the sub-Jurassic furrow, where a large area, to the SW, receives less than 900 mm. of rainfall per year. There is no dry season, but the rainiest time of year is summer, towards the SW. the autumn. A true climatic oasis is constituted by the shores of Lake Geneva, especially in the section between Lausanne and Montreux;
The climate of the Jura is harsh, with low winter temperatures and heavy snow; in some valleys the temperature inversion occurs. The winds of O. and NW. they discharge part of their humidity on it, so that it receives abundant rainfall although their values remain much lower than those of the Alpine region. The area of Basel enjoys a particularly mild and serene climate, which the Jura protects from the fog so frequent in the Altipiano area.
