The Weather Channel: You announce the return of cold from Sunday: will this cold be remarkable?
Régis Crépet : Polar air will invade France from Sunday, contrasting sharply with the relative mildness of the atmosphere at the beginning of December. We will lose around ten degrees across France between Friday and Sunday. The strong wind will turn due north, then northeast on Monday and Tuesday, accentuating the very cold feeling with the north wind. Temperatures will drop 4 to 6°C below seasonal averages. The cold will be widespread as far as the south with a biting mistral. However, this will not be anything remarkable for the season, although generally speaking, this type of weather usually occurs in the second part of winter rather than in December, with the famous showers.
Timeline of upcoming winter degradation © the Weather Channel
It is important to clarify that we will not speak of a cold snapa term which is increasingly in vogue as soon as temperatures drop in winter. This terminology meets strict meteorological criteria which will not be achieved (duration, intensity for example). The frost will be not very intense in the plains due to the clouds and the wind which will limit nighttime radiation, but the maximum temperatures will remain low. In the mountains, however, conditions will be fully wintery with intense cold and violent winds. It is above all the “feeling” which will be particularly cold during this episode.
temperatures felt low Monday and Tuesday afternoon © The Weather Channel
Does this cold look like it will last?
The cold will last all next week © The Weather Channel
The whole next week will be cold, the coldest day will probably be Wednesday with a national thermal indicator forecast at +2.6°C, which would be the coldest day since January 21. The afternoon maximums should be between 2 and 5°C over a large northern half, and 4 to 9°C in the south, where the deficit compared to normal will be the most marked. Nights are expected to see temperatures between -3 and +3, with -10°C in mountain resorts. This cold is expected to persist until the weekend of December 15. Then, a change in weather could set in with the return of the moist and gentle ocean flow from the west. This ocean flow could prevail in view of the Christmas holidays.
You announce the arrival of snow: should we fear an episode in the plains like last November 21?
Snow: the most exposed areas © The Weather Channel
We remember the exceptional snowfall for the season which affected the regions from Normandy to the Paris basin and to the east with the passage of the Caetano storm. This episode was linked to an air mass conflict between the rise of mild air in contact with the cold air present north of the Loire. This cold episode only lasted three days in these regions. This time, it is a flow of polar air which will invade all of France, a more classic situation.
The cold will be widespread and more pronounced, but the snow should not fall in abundance on the plains, rather in the form of heavy showers. This situation will, however, be more beneficial to our mountain ranges which will all be very snowy on this occasion.
As the Christmas holidays approach and a few days before the general opening of ski resorts, what thicknesses are planned?
Snow on the ground, thicknesses envisaged © The Weather Channel
The big winners of this winter offensive will be all our low altitude massifs. Between Sunday and Tuesday, they will be covered in a white coat from 700 to 800 m, sometimes less in the center east, the region most exposed to snow at very low altitude.
Around 1000 m altitude, we can expect 10 – 15 cm, sometimes 20 cm in the Vosges, the Jura, the Northern Alps and the north of the Central massif. This situation could complicate traffic conditions on roads such as the A75 and the A89 in the central massif.
Around 1500 m altitude, we expect 30 to 50 cm, especially in the Jura and the Northern Alps. the wind will form snowdrifts, adding predictable difficulties to the altitude network.
Around 1800 m, we could reach 1 m of snow in the Alps and the Pyrenees, with the formation of snowdrifts and dangerous snow cornices.
Finally, at very high altitude in the Northern Alps, thicknesses of 2 m of snow are plausible, superimposed on already abundant snow up there since the beginning of autumn. It is therefore a beneficial situation for the resorts, and for vacationers who are soon heading to the mountains.
