With the recent depressions which swept the west and north of the country, mainland France recorded, according to Météo-France, a record rainfall for 26 consecutive days.
Aline, Céline, Ciaran, Domingos… In just a few weeks, depressions and storms followed one another in France. So much so that the country broke a record for cumulative rainfall over 26 consecutive days, all seasons combined, Météo-France announced Monday, November 13. “Between October 18 and November 12, France recorded an average accumulation of 215.4 mm”, detailed the forecasting institute in a press release. On Tuesday, Pas-de-Calais and Haute-Savoie returned to red alert for the flood phenomenon and a total of 11 departments are on orange alert for floods and/or rain-floods.
Météo-France explains this “succession of almost continuous rainy periods” by a phenomenon of “rail of depressions”. This is’“a current of strong winds, called a jet stream, extended over several thousand kilometers in length in the Atlantic and located a few kilometers in altitude, which controls the trajectory of the depressions arriving in Europe”defines for franceinfo Loïs Pourchet, forecaster at Météo-France.
🌧️Thanks to a succession of rainy spells, France recorded from 10/18 to 11/12 (26 days) an average accumulation of 215.4 mm. This is the first time that the country has recorded such an accumulation over 26 consecutive days in all seasons.
➕more info: https://t.co/ZCW8Wy7ZCH pic.twitter.com/LugzF5P3vz
— Météo-France (@meteofrance) November 13, 2023
Every storm is a wagon
“Currently, this jet stream is positioned in a fairly straight line, it crosses the Atlantic Ocean,” explains François Gourand, forecaster at Météo-France, to Géo. The depressions follow one another practically without interruption due to this rail of depressions which “plays a major role in the activity and trajectory of mid-latitude depressions”writes Météo-France on its website.
“The depression rail is like a little train where each car is a depression.”
François Gourand, forecaster at Météo-Franceto Geo
“The marked temperature difference between high latitudes and subtropical regions allows the jet stream to rise from the Atlantic to Western Europe: this forms a corridor for rainy disturbances which form offshore and are brought to our doors by this classic configuration”, develops Météo-France.
From this “energy imbalance linked to temperature differences between a warmer tropical air mass and a colder polar air mass”, results “a strong wind at very high altitude supposed to rebalance the atmosphere, which creates a sort of highway reserved for storms heading straight towards the European coasts”details Loïs Pourchet.
Autumn, a favorable season
If the power of these depressions is quite exceptional in view of the precipitation records recorded, this depression rail is not a meteorological anomaly. “In the fall, the pattern of depressions sets in, because it is a changing season during which there is a cooling of the poles, but where we do not yet have complete cooling of the tropics”confirms to TF1 Lucien Vernezoul, forecaster at Météo-France.
“The orientation towards Western Europe is quite classic in autumn, but this gives rise to particularly remarkable episodes of rain.”
Loïs Pourchet, forecaster at Météo-Franceat franceinfo
The persistence of the orientation and intensity of the winds at altitude contributes to the storms which affect France and brings marked episodes of rain. “We have not observed a particular trend over recent decades”remarks Loïs Pourchet, who assures that the depressions are not over. “We should not expect a dry episode straight away. A new rainy disturbance arrives on Thursday, then Saturday in France with a fairly classic trajectory coming from the Atlantic coast, he warns. Regions already affected by floods “are not out of the woods”.