Swiss Plateau - Climate

Climate

The Swiss Plateau is situated within a transition zone between humid oceanic climate and continental temperate climate. The predominant wind comes from the west. In the lower plateau, the mean annual temperature is about 9 – 10 °C. In January, the lake Geneva region and the watersides of lake Neuchâtel and lake Biel have the highest mean temperature of about +1 °C. At the same height AMSL, the temperature is decreasing towards the east. In the lake Constance region, the mean temperature of the coldest month is -1 °C. In July, the mean temperature of Geneva is 20 °C, alongside the southern edge of the Jura it is 18 – 20 °C, and in higher regions 16 – 18 °C. With regard to mean sunshine duration, the lake Geneva region is again advantaged with more than 1900 hours, whereas in the rest of the Swiss Plateau, it is between 1600 (especially in the east) and 1900 hours.

The annual average rainfall is between 800 millimeters near the Jura, 1200 millimeters in the higher regions and 1400 millimeters at the edge of the Alps. The driest regions of the plateau are in the lee of the High Jura between Morges and Neuchâtel. In the warmest regions at the lakes of Geneva and Neuchâtel, there are less than 20 days with a snow cover, whereas in the rest of the plateau, it is between 20 and 40, depending on the height.

In the winter half year, the air on the Swiss Plateau can stay still, with little exchange to rest of the atmosphere, building a lake of cold air on the plateau and often a ceiling of high fog. The clouds look like an ocean of fog when seen from above, (usually around 800m) and hence is called the 'nebelmeer'. This weather is called inversion because the temperature below the fog is lower than the temperature above. Sometimes, it lasts for days or even for weeks, during which the neighbouring regions of the Alps and the Jura can have the brightest sunshine. Typical for the high fog is the bise, a cold wind from northeast. Since it is channelled by the Swiss Plateau narrowing in southwest, it reaches its major strength in the lake Geneva region where wind speeds of 60 km/h with top speeds of more than 100 km/h are usual in typical bise weather. The regions near the Alps of the central and eastern plateau sometimes have temperature rises due to the warm foehn wind.