‘Atmospheric river’ prompts flood and avalanche alerts in southwest France

An ‘atmospheric river’ is bringing concerted, heavy rain to southwest France, prompting warnings of flooding and avalanches in seven Pyrenean départements.

A man walks under an umbrella during a rain storm
A man walks under an umbrella during a rain storm. Several parts of France have been placed under 'orange alert' for the coming days. Photo: Pascal Guyot / AFP

National forecaster Météo-France has placed seven departments traversing the length of the Pyrénées mountain chain on orange alerts – its second-highest weather alert, which warns anyone in the area to be ‘very vigilant’.

The Pyrénées-Atlantiques and Hautes-Pyrénées are on orange alert for the risk of rain and flooding. The Gers, Landes and Pyrénées-Atlantiques are on orange alert for flooding. Finally, Hautes-Pyrénées, Haute-Garonne, Ariège and the Pyrénées-Orientales face an unusually high risk of avalanches for the season.

The unusually wet weather is being driven by a weather phenomenon known as an “atmospheric river” – a narrow corridor of concentrated moisture in the atmosphere – while a large sea swell along the Basque coast will block the flow of rivers into the Atlantic, which could lead to flooding upstream.

Atmospheric rivers are described by scientists as “long, meandering plumes of water vapour often originating over the tropical oceans that bring sustained, heavy precipitation to the west coasts of North America and northern Europe”.

It has the potential to cause long periods of sustained rainfall in winter months. The particular “river” causing heavy rain in southwest France is “at the end of its course” Météo-France said, but will still lead to very high precipitation in the coming hours. 

Between 50 and 70mm are expected by the middle of Friday in the Basque Country, and 80 to 100mm in the relief of the Pyrenees. But the level of rain and a rise in temperatures in the Pyrénées have also prompted an avalanche warning following several days of major snowfalls.

READ ALSO Winter weather: Pyrenees and French Alps set for more snow 

Météo-France said: “avalanche activity expected from Thursday afternoon to Friday morning is observed on average once every two years, but is atypical this early in the winter season”.

“These avalanches will be able to affect roads … and mountain infrastructure,” the forecaster warned in its latest bulletins. 

With the intensification of the rains, these avalanches will be able to carry away all the snow cover already in place. The peak of avalanche activity will coincide with the intensification of the rains and should begin in the middle of the afternoon for the massifs close to the Atlantic, in the late afternoon for the central Pyrenees  and in the early evening for the Pyrénées-Orientales.

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Just how hot is this week’s May heatwave in France?

Temperature records are tumbling as France swelters in an early summer hot spell - and forecasters predict more highs will be reached before any respite.

Just how hot is this week's May heatwave in France?

In the northern département of Manche, a département unaccustomed to high temperatures, the mercury reached 26C in La Hague on Tuesday, breaking a record for May dating back to 1922. The highest temperature on Tuesday across France was 32.8C recorded in Agen. But that record is not expected to last long.

Keraunos, the observatory for tornadoes and violent thunderstorms, warned that France could see a new national temperature record close to 37C between Friday and Sunday, some +17C higher than normal for the time of year.

According to national forecaster Météo France, temperatures were expected to hit 34C in Toulouse on Wednesday, beating the May record of 33.1C in the Pink City set in 2001, while Bordeaux was expected to see similarly high temperatures. Forecasters predicted 31C in Paris, compared to around 22C normally, while in the far north of the country, 29C was expected in Lille.

According to François Jobard, forecaster for Météo France, “since at least 1947, there has never been a ‘heat wave’ in May, because the hottest day in May remained well below 25.3 ° C (22.9°C: May 28, 2017). In fact, until now, this threshold has never been reached before a June 20…”

The reason for the unseasonably high temperatures? Since the beginning of May, France has been blocked under an anticyclone. “We are already seeing an anomaly of more than 2.7 degrees higher than average,” a Meteo France spokesperson told Franceinfo. 

Forecasters fear temperatures across the whole of the month could end up being 3C above normal. The hottest May on record was in 2011, when average temperatures were 1.85C higher than the average.

A European Commission report said the hottest May day since measurements began was expected on Wednesday, particularly in the Rhone valley.

Despite storms forecast for Wednesday in the north and west of the country, which are set to spread across France over the weekend, Météo France forecaster Gaétan Heymes said in a Tweet that it is “almost certain that this month will be drier than normal. Beating the 2011 drought record remains largely possible…”

That will mean nine of the past 10 months – December is the odd one out – have been drier than normal.

Meteorologists say the abnormal temperatures risk becoming more frequent in the coming years as a result of climate change.

“Heatwaves are set to become more frequent and tend to set in earlier in the spring than before,” Météo France said.