From -33 to 8°: a spectacular mild spell follows a white Christmas

The Combiers were able to remove their mittens on Saturday: renowned for its Siberian temperatures in winter, the Combe des Amburnex, very close to the Col du Marchairuz, went through two seasons in less than 24 hours. Saturday morning, a chilly -33° was measured there. At 5 p.m., the thermometer showed 2°. The next day, 8.2°.

Although it was less extreme than at the Amburnex, the phenomenon was particularly marked along the entire length of the Alpine arc. At an altitude of around 3,000 m, on the slopes of the Diablerets glacier, the temperature went from -10° on Saturday morning to 0° a few hours later. At 1670 m, on the Dôle side, the mercury jumped from -5° to 6°, between Saturday and Sunday. In Adelboden (BE), a peak was measured at 14°.

“The night from Friday to Saturday was the coldest of the winter at this stage, including in the plains where -10° was recorded,” explains Vincent Devantay, meteorologist at Météonews. A warm front followed Saturday during the day and the snowfall limit rose to 2300, even 2500 m above sea level.” In the plains, we gained 15° in places. “This type of mild spell is not unprecedented, but such deviations remain rare,” continues the meteorologist. At this time, we are more accustomed to seeing the 0° limit rise to 1500-2000 m, whereas on Sunday, it flirted with 3000 m.”

Accelerated melting

Added to this sudden increase were foehn and high humidity: “The factors leading to rapid melting were combined,” explains Vincent Devantay. At Moléson, the snow cover lost 30 cm in 12 hours.”

After the success of a particularly white Christmasmid-mountain resorts have suffered the full brunt of this meteorological turnaround. In the Vallée de Joux, the snow report states: “Facilities closed until the next snowfall, the rain and the mild weather have damaged the alpine ski slopes!” Others have also had to resolve to temporarily disconnect their ski lifts, like Rasses, Saint-Cergue and Moléson (FR).

“The snow cover was not spared here,” testifies Gérald Gygli, president of the cooperative which operates the Pléiades lifts. We decided to close to save what’s left.” For the small destination on the Riviera, this change fortunately comes at the least bad time: “We were able to open during the holidays, with the exception of two days at New Year’s. On Saturday, we were overflowing. Of course, this mild weather disappoints us, but we are not worried at all.”

Especially since the flakes could quickly make a return. “The snowfall limit will play yo-yo over the next few days, but we are expecting snow again at the end of the week,” says Martin Deburaux, director of Télé Villars-Gryon-Diablerets. Despite the temperatures of the last few days, we are skiing well and returns to the resort are assured.”

Return of snow at 2000 m

In mid-altitude resorts, we are monitoring the weather, hoping for the return of snow, but Vincent Devantay remains cautious in his forecasts. “The peak of mildness has passed and a disturbance follows it. The snowfall limit will drop to 1800 m then to 1200-1300 m during the night from Monday to Tuesday, to rise to 2000 m on Wednesday, before falling at the end of the week. We can expect a fresh layer of 18 to 30 cm in the Vaudois Alps and in Valais, above 2000 m. But the precipitation will be less abundant at the end of the week.”

Avalanche danger remains high

Heavy snowfall, followed by a strong mild spell, wind and a rain-snow limit that plays like a yo-yo: the meteorological cocktail is explosive in the mountains. Monday morning, the Alpine arc was tinged orange, on the maps of the SLF, the Swiss institute for the study of snow and avalanches, i.e. a “marked” danger. The situation is less tense than the day before: “The situation is evolving day by day,” explains Pierre Huguenin, head of the Valais branch of the SLF. The peak of danger induced by the mild weather of the weekend and the foehn seems to be behind. Further snowfall is expected during the week, but not phenomenal quantities: we are talking about 20 to 30 cm, depending on the sector. Temperatures will yo-yo over the next few days and we expect a return of sometimes strong westerly winds. Despite everything, we should remain at a degree 3 danger, as currently.”

By Christmas, the SLF maps had turned red, particularly south of the Rhône, due to heavy snowfall on fragile bottom layers. “But these layers are now better buried and the situation is stabilizing in this region.”

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David Genillard has been a journalist in the Vaud & Régions section since 2007. Based in Yverdon since 2023, he mainly covers news from Northern Vaud. In 2021, he also participated in the launch of the weekly Riviera-Chablais Votre Région, a 24-hour partner.More info

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