How do you explain this large temperature difference?

An unusual temperature difference? For 19 consecutive days (from November 30 to December 18), the national thermal indicator therefore remained below the 1991-2020 averages. In particular, there was a cold peak on December 17, when the temperature even reached -19°C in the early morning hours in the Lorraine countryside. It was necessary to go back to 2010 to find such a cold December. Indeed, the -5°C recorded in Paris on Sunday morning had not occurred since December 1996. In question, an anticyclone positioned over Scandinavia directing a north-easterly wind, at the origin of this mass of cold air coming from Russia.

But on this Monday, December 19, France experienced very mild weather, due to a change in the meteorological configuration. The anticyclone has retreated towards central Europe. This gave way to a depression over the nearby Atlantic. This time he drove a vigorous southwesterly wind carrying a very mild air mass from the Canary Islands and Morocco, where it was 25°C this Monday afternoon, December 19th.

Read also: Weather: why such a sudden drop in temperatures this week?

A remarkable and rapid thaw

The rise in mercury has been impressive in places. This is the case of Épinal, where only -12°C was measured this Sunday December 18 at 8:00 and where the temperature has already reached 8°C this Monday at 1:00, or more than 20 degrees below 24 hours. During the day the temperature then continued to rise until it reached a maximum of almost 13°C.

In Paris, from -5°C on Sunday morning, the temperature practically didn’t stop rising until it touched 12°C this afternoon. The highs rose 10 degrees above the season average in places.

Also, mildness will have been particularly marked earlier in the week in the Southwest. In fact, temperatures exceeded 20 degrees at the foot of the Pyrenees. We also recorded 9°C in Lille, 12°C in Paris, 14°C in Rennes, 15°C in Lyon and 17°C in Bordeaux, Toulouse and Biarritz.

Only northern Alsace still recorded below-normal maximum temperatures on Monday.

Not an exceptional temperature difference

Nothing exceptional or abnormal about this temperature difference according to Meteo France. It is above all the very cold period of recent days that has surprised. This phenomenon is becoming increasingly rare in a context of global warming. Such cold days as those experienced in the last two weeks have become increasingly exceptional over the past decade. However, they may still occur in the future.

Furthermore, after an October with broken temperature records, and also a mild November, this winter sequence was all the more surprising. Just like the sudden rise in mercury, a situation we would have almost lost the habit of.

However, this weather reversal itself is relatively classic in its pattern. Despite everything, this is not necessarily the case in his particularly accelerated times, which are in fact more unusual.

A very sweet Christmas ahead

This noticeable thaw will continue throughout the week, leading up to the Christmas weekend in rainy weather. A parade of perturbations is expected, with rainy passages in the north: soft and humid ocean air, therefore.

For the next few days, temperatures will be about 5°C above national averages, and sometimes 8°C in the southwest. We shouldn’t reach sweetness records for a month of December. In 1989, for example, they stood at 17°C in Paris, 20°C in Lyon and 22°C in Clermont-Ferrand.

Thus, this Sunday, the opening of the gifts should take place in soft and rather calm conditions. Hazy to cloudy atmosphere, waiting for the new perturbation that would arrive from the north-west at the end of the day. Likewise, inputs from the sea will return to the Mediterranean. They would be accompanied by a flow that should be oriented in the south-southeast sector.

The trend for the coming week appears to be gradually becoming more reliable. There should now be a majority of favorable scenarios for the continuation of relatively mild weather. However, others, more in the minority, see a possible change in the weather after December 28th. An anticyclone would swell over Scandinavia and could bring cold air towards northern France. Keep on.

Read also: December skies: magnificent observations in perspective