Winter storms in Switzerland
Winter storms affect Switzerland in the period between October and April. They arise as a result of significant differences in temperature and pressure which can occur in connection with the movement of the polar front (boundary between hot tropical and cold polar air) over Europe. On weather maps, prominent frontal zones can be recognised from the high number of isobars (lines of the same pressure) in a small area.
The hurricane-like winds, which mainly originate from a westerly direction, have a very extensive effect – the path of winter storms can extend over several hundred square kilometres, be up to 200 km in length and unfold over several countries. They usually last between one and several days. They generally affect all of Switzerland although they are less common in the south and east than in the northern and western areas of the country. The strong squalls that arise during winter storms are mainly responsible for their destructive effect: the strong gusts of wind, which occur for short periods, can reach top speeds of up to 250 km/h, i.e. double the average wind speed during a winter storm. With regard to the force of the winds, the doubling of wind speed corresponds to a quadrupling of force.
No other form of storm can cause as much damage in the course of a single event in Switzerland as a winter storm. The strong winds bend the branches on trees or uproot entire trees and damage parked vehicles and the roofs and facades of buildings. In extreme cases, the wind squalls can also damage the structural elements of buildings and cause them too collapse, thereby destroying them completely. Disruptions to transport routes and electricity supplies are also frequent consequences of winter storms. Free-standing objects carried along by the wind can also pose a threat to people who are outside during storms.
Extensive damage mainly results form winter storms in particular when the wind throw affects large areas of forests with a protective function (protective forests). Individual buildings can also suffer extensive damage as a result of the penetration of water into the building interior, the impact of falling trees and the blowing away of roof tiles.
The winter storms of the years 1990 (Vivian), 1999 (Lothar) and 2007 (Kyrill) also demonstrated the extensive nature of the damage to material assets and, unfortunately also, human life that these natural events can cause.