Weather forecast: one of the coldest first day of winter in 15 years – archyde

It is in season, but the cold wins all over France on Tuesday. The entire metropolitan area is affected by winter temperatures with sometimes severe frosts at daybreak.

“The weather is very cold at the start of the day with almost generalized frosts in the land, down to -3 ° C to -5 ° C from the Grand Est to Limousin and Auvergne Rhône-Alpes, as well as in the interior of Provence ”, specifies Meteo France. In some of the traditionally colder regions of the country, which are at an altitude of around 1,000 meters, the thermometer sometimes dropped significantly lower on Tuesday morning.

The clearer sky than in recent days favors the drop in temperatures at night: the warmer air, generally present near the ground, can easily rise because it is less dense and therefore lighter than cold air.

This does not prevent certain regions covered with clouds from experiencing low temperatures, sometimes more than at altitude. Why ? Sometimes a mass of air that is hotter and drier than the ground is already present at altitude. If, in addition, low clouds have formed, the cold air remains stuck to the ground. This phenomenon is called a “temperature inversion” since the normal situation is for the air to become colder and colder with altitude.

This inversion once again occurred this Tuesday morning in the Alps and sometimes causes “seas of clouds”. They are pleasant to observe from above with an immaculate blue sky and lower clouds, but more unpleasant to undergo on the ground with a grayness that does not go away, as shown in this photo taken last week from Alpe d ‘Huez (Isère).

The fact that temperatures drop yet another notch on Tuesday is caused by a breakthrough of cold air from Siberia to Eastern and Central Europe. France is on the fringes of this area affected by a cold snap, as shown in this map relayed by the meteorologist Guillaume Séchet.

Strictly speaking, however, the country was not affected by a cold snap. It is not cold enough and not long enough. As recalled Meteo France, “A cold snap is a lasting and extended episode of cold (at least three days). For an episode to be identified on a national scale, the national average temperature must drop at least a whole day below a certain threshold (-2 ° C). Cold waves are also characterized at the scale of a region when the episode lasts at least two days and the temperatures reach values ​​well below the seasonal norms of the region concerned ”. In addition, from Thursday, under the influence of a mass of air from the Atlantic, temperatures will rise by several degrees.

Regarding the only day of this Tuesday, Francois Jobard, forecaster at Météo France, considers that it could in any case become the coldest winter solstice for fifteen years.

Even if that did happen, however, it would be “anecdotal”, he says. On the one hand, this would only concern, from a statistical point of view, a single day, and would not say anything about the climate in general. On the other hand, this would absolutely not augur cold, hot, or average weeks to come.