MeteoSwiss expects mild winter despite weaker polar vortex
Keystone-SDA
The Swiss meteorogical service has played down speculation about a “winter of the century” this season.
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MeteoSwiss are expecting a mild winter, according to an enquiry from Keystone-SDA.
A rare weather phenomenon over the North Pole has sparked rumours of a harsh winter in Europe and Switzerland. This is known as sudden stratospheric warming (SSW).
Normally, a strong polar vortex holds the cold air over the Arctic. If it weakens, temperatures in the stratosphere, the layer of air at an altitude of around 10 to 50 kilometres, can rise by up to 50 degrees Celcius within a few days. This can change the polar jet stream and increase the likelihood of cold spells in several regions of the world.
MeteoSwiss confirms that the polar vortex over the Arctic is currently weakening and deforming at an altitude of around 30 kilometres. Over the next two weeks, the temperature in this layer of the stratosphere is likely to rise significantly.
According to MeteoSwiss, such an event has only been observed this early in the season three times in the last 70 years (1958, 1968, 2000).
Uncertain forecast
However, according to MeteoSwiss, the consequences of this for winter weather in Switzerland remain to be seen. The decisive factor is whether the changes in the stratosphere even make it into the troposphere – the layer of air that is relevant for our weather.
Moreover, it is often North America rather than Europe that is affected by the associated outbreaks of cold air. The polar vortex could also form again, so possible effects cannot be extrapolated for the entire winter.
Nothing has therefore changed in the seasonal outlook so far. According to MeteoSwiss, the probability of a cold winter in Switzerland overall remains rather low for November to January.
Few deviations from the long-term average are expected for December, but a high probability of above-average temperatures for January and February.
However, unlike weather forecasts, seasonal climate forecasts are subject to a high degree of uncertainty. The quality of long-term forecasts for central Europe and therefore also for Switzerland is still limited.
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Translated from German by DeepL/mga
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