A noteworthy episode of rain before Sunday: what to expect?

TO Regis CREPE, meteorologist

After a week of calm weather, marked by the persistence of the anticyclone over Central Europe, the troughs are approaching France both from the Atlantic arc, but especially from the Mediterranean. This weekend in the south-east of our country, a long period of very inclement weather is set, which may continue into next week.

The weather situation is changing. After the beginning of the week, marked by a brief cooling on the side of the cold wave that reigns over Eastern Europe, the flow heads south and brings soft air over the country. This development is facilitated by the retreat of the anticyclone and the approach of the Atlantic depressions. But this situation will remain blocked for several days, probably until next week, and the depression circulating over the Balearic Islands will cause locally intense rains around the Mediterranean accompanied by a sensitive easterly wind.




On the way to the Cévennes and the Mediterranean episode


concept of somethingEpisode of Cevenna usually attributed to autumn, when the masses of soft and humid air, weighed down by heat, coming from the Mediterranean, pour heavy rains in the Languedoc-Roussillon and especially in the Cevennes. When an episode is distributed to more regions, it is calledmediterranean episode.


For this weekend, various numerical models highlight this type of episode in association with several depressions located in the Iberian Peninsula and the Balearic Islands. This will shift the winds from the south to the southeast sector over the Mediterranean Basin, which will contribute to the rise of heavy rains towards the Gulf of Lion. It appears that the departments extending from the Eastern Pyrenees to the Cévennes, and also east of Corsica, are most affected by these heavy rains, with good agreement on the maximum intensity falling on the Cévennes. As of today, the estimated accumulations over the two weekend days are estimated between 150 and 300 mm on the reliefs of the Cévennes, which still leaves an error that we will clarify in our next updates. But these accumulations are important and especially concentrated between the night from Friday to Saturday and Sunday morning. It should also be noted that these heavy rains can giveheavy snowfall heavy and wet in the Cévennes and Eastern Pyrenees from 1400 m. We released weather alert on this topic.




Atypical situation for the season


Episodes of the Cévennes and the Mediterranean usually take place in autumn. Some sometimes work in the spring, and more specifically in May, when thunderstorms begin to form. It rarely stays in March. But if the centers of action are arranged in such a way as to cause a southerly current over the Mediterranean, the Cévennes episode is possible even at this time of the year. In March, this happens on average once a decade, the last series is dated March 2011 and March 2013, while the accumulations reach 150–200 mm in the Cevennes and Roussillon. In the past, the Cévennes had occasional rains in March 2004, 1999, 1996 and 1986, then especially in March 1969 and 1971, when significant rain fell, but not exceeding 300 mm in two days. If the episode modeled for this weekend is confirmed, the intensity will be significant for this time of year.


It should be noted that although this is rare in March, the past teaches us that the most severe flooding that occurred in metropolitan France occurred in the month March 1930 At the beginning of the month, catastrophic floods affected the Tarn Basin (100-year flood) and the Garonne, killing hundreds of people. It was the most intense natural disaster caused by a large-scale Mediterranean episode in addition to the rapid melting of snow cover.




The threat of bad weather and flooding in the Iberian Peninsula


In this configuration, the Iberian Peninsula will also be subject to heavy rainfall due to the location of the depression directly above Spain. After an exceptionally dry winter, the driest since 1962 in January and February, these expected heavy rains are good news for filling dikes, which are sometimes nearly dry but can cause flooding due to seepage on hardened soils. However, this weekend, the accumulations will not be more than in the Languedoc-Roussillon, but strong storms will break out throughout the territory, from Galicia to Andalusia through Portugal. Next week, while France could see relative calm, heavy rains could continue in Spain until Wednesday, potentially leading to flooding.


Rain and sandstorm in the Maghreb next week


North Africa has already suffered from notable episodes of rain since last weekend, especially in Morocco, where the coast sometimes received more than 100mm of snowfall, with a lot of snow in the mountains at 1500m above sea level on the Atlas. Bad weather is expected to resume early next week. In Algeria, rainy periods are currently more moderate and the sirocco, which will intensify, is likely to cause a sandstorm this weekend. But there, too, a very worrisome episode could continue for most of next week, especially in Morocco, where floods are also likely. All countries bordering the Mediterranean will experience heavy rains for at least the next eight days.


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