Tornadoes are very violent but spatially limited cyclones. They arise in association with extremely strong thunder cells and, due to the enormous local wind speeds involved, can leave considerable trails of destruction in their wake. Compared with tropical storms, which do not arise in temperate latitudes are, they are considerably shorter in duration and smaller in scale.
According to recent assessments, between one and five tornadoes may be expected to cause major damage in Switzerland over the course of a decade. Weak tornadoes can even arise several times per year. Hot summer days with strong storm probability are also a precondition for the formation of tornadoes in Switzerland. Hence, tornadoes mainly arise in June and August.
The western Jura, an area known to be prone to thunderstorms, appears to offer particularly advantageous conditions for the formation of tornadoes. The biggest accumulation up to now has arisen in the Vallée de Joux (Vaud) and in the region around La Chaux de Fonds.
For example, on 26 August 1971, a strong tornado hit the Vallée de Joux and destroyed numerous houses and entire tracts of forest over a 23-km stretch. Additional documentation (in German) about tornadoes in Switzerland can be found here.