Meteorologists said they observed an exceptionally early disruption of the polar vortex on Friday, which increases the risk of cold waves throughout the northern hemisphere, even if the consequences are still uncertain.
The polar vortex is a vast phenomenon of very powerful winds circulating between 10 and 50 km altitude above the Arctic during winter in the northern hemisphere.
Variations in its intensity and configuration (shape, temperature, etc.) can have consequences on the weather, leading, for example, to a significant drop in temperatures.
These winds strengthen in autumn until reaching their peak in January. The polar vortex can weaken in the second part of winter, usually between January and March, allowing extremely cold air to descend south and affect Europe, North America and Asia. But according to scientists, the vortex is already weakening at the beginning of November.
“To our knowledge, this is the earliest stratospheric vortex disruption ever observed,” Tim Stockdale and Frederic Vitart of the European Center for Medium-Range Weather Forecasts (ECMWF) told AFP.
The disruption of the vortex “considerably increases the risk of cold waves in the most populated regions of the northern hemisphere, the United States, Europe and East Asia,” specifies Judah Cohen, a climatologist at the Massachusetts Institute of Technology, interviewed by AFP.
Such precocity “is exceptional”, adds Grahame Madge, spokesperson for the British Met Office. A possible explanation would be “the amplitude of the El Niño phenomenon in the Pacific” this year, he adds.
Concretely, what does this mean for Switzerland? The polar vortex acts a bit like a barrier that helps keep the frigid air near the North Pole. When it weakens, this barrier can become less effective and encourage cold air movements towards the south. Switzerland could then experience lower temperatures, or even episodes of wind. But this does not necessarily mean that it will snow: everything will depend on how the situation develops in the coming weeks.
The polar vortex, when it weakens, can modify the circulation of winds in the atmosphere and promote the arrival of cold air in Europe. But its effects are neither immediate nor systematic: it is difficult to precisely predict the consequences on the weather.
This development can in particular favor weather situations which last several days, as well as easterly winds, likely to bring cold air. However, this does not mean that a cold snap or snowfall will necessarily affect Switzerland.
In the short term in any case, it is rather a slight warm spell that is expected, with for example temperatures which could reach 15 degrees in the Lake Geneva region in the middle of next week. We will know in the weeks that follow whether the early disruption of the polar vortex will cause us particularly cold winter episodes.
