snow from Brittany to Alsace, up to 10 cm and dozens of vigilances this Thursday

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In some homes, Christmas is a long time coming (and in your home, the tree may even already be out and decorated). To top it off, the first snowflakes of the season will fall on the plains this Thursday, November 21, 2024, and Météo-France has already placed many departments on orange alert for snow-ice.

The fault of storm Caetanowhich “will cross France from west to east”, with snow on the plains, “and cause an early and sufficiently notable winter episode to make traffic conditions difficult in the regions concerned”, anticipates the French weather organization , in a press release.

An air mass conflict

This is what Guillaume Séchet, meteorologist and founder of the site Météo-villes.com, confirms. “Snow is well linked to a depression which is rising over France, which will move between the Loire and the Seine,” explains the specialist, contacted by actu.fr.

This Caetano depression is linked to an air mass conflict between cold air which descends from the North Pole over the entire northern part of Europe and milder air from the Canaries, which resists to the south, particularly over the near Atlantic. . There will really be this standoff, with France at the heart of this conflict. But it's the cold that will prevail, bringing snow to the plains here.

Snow between Brittany and Alsace

Quid areas concerned? We know that the regions Brittany, Normandy (“except Seine-Maritime”, according to the forecaster), northern Pays-de-Loire, southern Île-de-Franceet Centre (in the plains), will be affected.

“But the problem is that depression is capricious, and we still don’t know exactly its trajectory. However, it is on its trajectory that the regions affected by the snow depend, over an area approximately 200 km wide to the north of the depression precisely,” explains Guillaume Séchet. They are therefore required to evolve, “this can vary over 50 to 150 km”.

A priori, the snow in the plains will start to fall this Thursday morning in Brittany and Lower Normandy to spread towards the center and Ile-de-France at midday, and evacuate towards Burgundy and the Franche-Comté in the afternoon and evening.

Note that Caetano will also train (south of the depression) “a storm between the Atlantic coast and Limousinwith gusts around 100 km/h inland, towards Poitou-Charentes and the Massif Central.”

A good layer of snow in certain areas

But then should we expect heavy layers of snow and polar cold? “It will be between 0 and 1°C in the regions where it will snow, but again there is a bit of uncertainty,” according to Guillaume Séchet.

Estimates confirmed by Météo-France, which even anticipates 2 to 5 cm locally “in northern and central Brittany and the interior of Normandy where accumulations could reach 10 cm on the Normandy hills“, as we can read in a press release.

1 to 3 cm (will be) possible in Paris – Petite Couronne, up to 7 cm in Essonne and more in the regions further east and at altitude (up to 20 cm near Belfort).

“This snow will be particularly wet and could pose problems for transport,” anticipates the meteorological organization.

According to the forecaster, the snow will be heavy and should stick to the ground, “even in cities, like Le Mans (Sarthe), for example, only to melt the next day, or even Saturday.”

Yoyo the weather between Thursday and Saturday

On the other hand, the weather will be more stable from Friday. “The mild air will take over on Saturday, it will be very powerful, and on Sunday, we could even beat softness records in Paris in particular (where we wait 18-19 degrees). It seems incredible, but we are going to have a huge yoyo between Thursday and Saturday,” adds the meteorologist.

However, the snow on the plains that the French will experience this November 21 is a rather classic phenomenon, “it even happened that it snowed on the plains at the end of October”.

However, in recent years, it has become increasingly rare; it occurred more frequently 30-40 years ago. The fault is global warming, and the two additional degrees that we know today.

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