The climate of Switzerland is strongly influenced by the nearby Atlantic. The predominantly westerly winds transport moist and mild maritime air into Switzerland. This air has a cooling effect in summer, a warming effect in winter, and it ensures that there is enough precipitation in most regions throughout the year. The Alps thereby act as a pronounced climate barrier between Northern and Southern Switzerland. Southern Switzerland, which is mainly influenced by the Mediterranean Sea, is characterized by much milder winters than Northern Switzerland.
Drier climate in the central Alps
The dominant climatologic effect of the Alps is that of a barrier between the North and the South. However, due their complex structure, the Alps additionally generate several different climate regions on their own. Especially the valleys in the central Alps have their own distinct climate, because they are shielded against precipitation both from the north and the south, leading to dry conditions. This is for example clearly the case in the Valais region in Southwestern Switzerland and in the Engadin re-gion in Southeastern Switzerland. Indeed, along the northern Prealps and Alps, as well as in Southern Switzerland, an average precipitation amount of about 2000 mm/year is observed, which contrasts with the amounts observed in the Valais region (between 500 and 600 mm/year) and the Engadin region (between 600 and 700 mm/year). In the lowlands north of the Alps, the average amount is between 1000 and 1500 mm/year. Apart from the Valais region, the amount of rainfall in summer is approximately twice as large as that in winter.
Snow in winter
At altitudes higher than 1200 to 1500 m a.s.l., winter precipitation mainly occurs in the form of snow, so that a closed snow cover can often be observed for several months. In contrast to that, snow is only relatively rarely observed in the lowlands of Western Switzerland (Geneva region) and Northern Switzerland (Basel region) as well as in the lowlands in the far south of Switzerland. In these regions, it is not unusual that there is no snow cover at all in winter.
Temperatures - from arctic to mediterranean
The temperatures in Switzerland primarily depend on the altitude. In the northern lowlands, the average temperature in January is approximately 1°C and in July approximately 17°C. The corresponding average temperatures in the southern lowlands are 2-3° higher. At altitudes of approximately 1500 m a.s.l., the average temperature in January is about -5°C and in July about 11°C. Considering those locations in Switzerland where a series of observational data is available, Locarno-Monti in southern Switzerland is on average the warmest place with an annual mean temperature of 11.5°C. The coldest place, on the other hand, is the Jungfraujoch, located at 3580 m a.s.l., with an annual mean temperature of -7.5°C. The highest temperature that has ever been recorded in Switzerland, namely +41.5°C, was observed on 11 August 2003 in Grono in Southern Switzerland; the lowest temperature, -41.8°C, was measured on 12 January 1987 in La Brévine in the Jura Mountains.
Foehn as a special climate component
A special peculiarity of the Swiss climate is the well-known foehn. This cross-Alpine wind flow induces mild and dry conditions on the respective lee side of the mountains. Especially the “south foehn”, which blows from the south to the north, is often characterized by high wind speeds in the north and intensive rainfall in the south. It is especially in the time between autumn and spring that foehn winds occur.