Like the air of spring, just after the first frosts. While the mercury fell below zero on Thursday, November 21, it will rise sharply this weekend. The Caetano storm which crossed France from west to east caused a “early winter episode”according to Météo-France. Snowfall was observed over a large part of France and freezing temperatures were recorded. The thermometer thus displayed –10.8°C in Bourdons-sur-Rognon (Haute-Marne). But the temperature will quickly rise, because Météo-France announces “a powerful redoux” starting Saturday afternoon. Temperatures could rise to 20°C on Sunday in the north of the country and 25°C in the Basque Country, according to the forecast institute. Franceinfo takes stock of the sequence of these two contrasting weather sequences.
1 What will the weather be like this weekend?
The weather will be very mild this weekend, with temperatures going above 15°C in the northern half of France, and even 25°C on Sunday in the South-West. “These spring temperatures will be locally accompanied by violent winds over Brittany, the Pyrenees, the Massif Central, the Saône Valley and the Rhône Valley.specifies Jérôme Cerisier, meteorologist at Weather Solutions. The gusts, expected from Saturday, should however be less strong than during the passage of storm Caetano. They will strengthen on Sunday.
Temperatures will rise sharply from Saturday afternoon and will continue to rise on Sunday, reaching “between 6 and 9°C above seasonal averages”notes Jérôme Cerisier. “We will be able to approach daily or ten-day records [mesurés sur une période de dix jours], but it’s not extraordinary either.” It is above all the contrast observed locally in a fairly short period of time that is striking: in certain localities, the thermometer will have risen by 10 to 15 degrees in forty-eight hours.
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2 How to explain this warm spell?
This transition from cold to mild is explained by the movements of two different air masses. “We are going to completely change the air mass regime. Since Thursday we have had a polar air flow, arriving directly from the Arctic. From Saturday morning, we will observe the arrival of the Bert disturbance, which will cause storms over the British Isles Ahead of this disturbance, we have a gentle flow.explains Jérôme Cérisier. “It’s a bit of a yo-yo, it’s noticeable, but it’s already been seen during the off-season”contextualizes the meteorologist.
It is this subtropical air mass, coming from the Canaries and the Maghreb, which will cause the mercury to rise. These southerly winds will also cause significant gusts in Brittany, in the Pyrenees, the Massif Central, the Saône Valley and the Rhône Valley.
3 Will this episode last?
This peak of mildness should last forty-eight hours, before the weather stabilizes. “From Monday afternoon, a disturbance from the west will cross the entire country. It will be mild in the morning, then the rain will bring a drop in temperature”announces Jérôme Cerisier. We should therefore return to measurements closer to the season averages. But this time, temperatures will drop gradually, over the course of the week, and not as suddenly as last Thursday. Monday afternoon, Météo-France announces 12°C in the North and up to 20°C in Corsica and 17°C in Nice. Tuesday morning, temperatures will rise to 8 or 9°C in the northwest quarter and 13 to 15°C in the Provence-Alpes-Côte d'Azur region.
