Down jackets and hats are to be taken out of the closet: after several weeks of mild temperatures, the mercury will drop by 10°C nationwide in the coming days.
In question, the polar vortex, this natural meteorological phenomenon formed by a large depression whose temperature varies with the seasons, and which intensifies at the time of the winter season, explains Météo France.
Wind circulation reverses
Confined to the poles, the polar vortex is traditionally kept over the Arctic region, at an altitude of about 30 kilometres, by circular winds that circulate very quickly from west to east in winter: these are the "stratospheric jets of the polar night". These winds reinforce the jet stream, a famous current present in the atmosphere of planet Earth and whose influence is decisive on the weather.
However, the circulation of these fast-moving winds can sometimes reverse, to the point of weakening or breaking the jet stream. The cold air from the polar vortex is then carried to lower latitudes, unaccustomed to such cold waves: this will be the case in the coming days in Europe.
In France, temperatures will gradually drop over the week, and will reach their lowest peak level next Tuesday, which could be the coldest day since February 2018 according to Météo-France. In the afternoon, temperatures will be negative in a large part of the country, and will not exceed 0 degrees in Paris, Nantes, Tarbes, Metz or Lille, details La ChaîneMétéo*. This polar vortex had already hit Europe in March 2018, and France in February 2012.
*The Weather Channel is owned by the Le Figaro group.