1Meteobüro und Bildagentur - Switzerland
2Institute for Atmosphere and Climate, IACETH - Switzerland
Funnel clouds and similar whirls often develop in association with strong winds or deep convection. These funnels may or may not be precursors of tornadoes (or waterspouts). Many of these funnels are short-lived and hardly visible, due to dust, rainfall, or a hilly orography. Therefore, almost all funnels probably remain undetected, at least in regions where the public is not aware of these phenomena. A better detection rate could contribute to a better understanding of tornado climatology since these precursor events are much more frequent than the stronger tornadoes. It is therefore our goal to promote a better conciousness for funnel clouds in the public, and to collect all observations of funnels during a multi-year period. Reported events are summarized on our web-page www.meteoradar.ch/tornado, which is part of the TorDACH-project.
In 2000, 4 torndoes and 3 funnels are documented in Switzerland. In 2001, 6 funnels and 1 tornado have been observed. Here, we present several observations obtained within 2000 and 2001.
On 5 June 2000 a tornado was observed by several persons near Wetzikon (SE of Zurich). That tornado was associated with a heavy hailstorm originating in central Switzerland and propagating towards NE.
On 21 October 2001 a funnel was observed over the Lake Constance. On that day, a cold front terminated a period with warm temperatures. A mini-supercell propagated from W to E through northern Switzerland. Hail damage was registered which is very unusual for that time of the year. The funnel occured within a gust front producing high wind speeds.
On 7 Feb 2001 southerly winds over the Alps led to "Föhn" in the valleys north of the Alps. Wind speeds up to 130 km/h were registered in the Reuss valley close to the southern part of Lake Lucerne. The shore of that lake is very steep and rocky. Whirls were shedded away at rocky "noses". After that, the whirls drifted over the lake like waterspouts.
Fotos are available from some events and will be shown on the poster, together with radar images and a short description of the meteorological environment. In summary, we conclude that the events are very diverse. No common "denominator" can be seen. Therefore, there is a need to collect much more cases, in order to obtain a statistically valid data sample.