All fashion buffs and weather app addicts will tell you: the fall 2023 trend is umbrellas. Météo-France recorded an average cumulative rainfall of 215.4 mm over 26 consecutive days, straddling between mid-October and November 12. A record, all seasons combined. How to explain such a phenomenon ? Will the sky continue to fall on our heads? Should we be happy or worried about such an episode? Elements of response with Frédéric Long, forecaster at Meteo France.
How do you analyze this precipitation record?
The fact that it rains a lot after a long dry period is not in itself exceptional. This remarkable accumulation can be explained by a series of disturbances over this period, with little respite between these episodes. Over this period, exceeding 100 mm remains normal. But going beyond 150 mm is much rarer. As for passing the 200 mm barrier, this is the first time that we have seen this since the establishment of cumulative readings in 1958.
Emmanuel Macron is present this Tuesday in the Pas-de-Calais department, heavily affected by flooding. Is a lull in sight in the coming days in this territory?
This Tuesday, at the beginning of the afternoon, fairly intense rain is forecast and will not improve the situation. These disturbances will continue to circulate for the rest of the month, it is a little early to say if they will be less active. For the moment, we do not see come lasting dry period in the territory.
What is a “depression rail”, one of the causes of this continuous rain?
It is the limit between the mild air of subtropical origin and the cold air of polar origin which undulates at our latitudes. The air mass contrasts are quite marked in autumn with mild air and already cold air over northern Europe. The previous record for cumulative precipitation also fell in autumn (196.9mm between September 21 and October 16, 1993). In winter, the mild air becomes rarer, so there are fewer moisture reservoirs. In spring, we more often have precipitation in the form of showers or thunderstorms, not precipitation that passes by like at the moment.
Should we be worried or happy about this regular episode of rain?
Hard to say. In France, we are coming out of two dry years, it is rather positive that the rain is falling. But the observation needs to be qualified. To the east of Corsica and around the Mediterranean, rainfall totals are below normal. It has sometimes rained on the terrain (Cévennes, Southern Alps) but the soils remain drier than normal in certain departments, notably in the Pyrénées-Orientales. Then, what fell is not homogeneous throughout the country, with regions more or less vulnerable to the risk of flooding.
What should we expect for the rest of November?
We’re not going to put the umbrella away just yet. For the next few days, the disruptions will continue to unfold. On the other hand, temporarily, it will be a little drier. Tomorrow (Wednesday), the rains will not be very marked, but a new active disturbance will cross the country on Thursday. There will be a lull on Friday, before yet another disturbance this weekend. There is no high pressure coming in the next few days.
France has suffered two big storms (Ciaran and Domingos) in recent weeks. Are others expected?
A storm is difficult – if not impossible – to predict several months in advance. It forms and circulates very quickly, we generally manage to see it a few days before. For this weekend, having periods where pressures rise a little can lead to depressions which circulate at fairly high radians, which can lead to a few gales, but not storms.
With climate change, the IPCC predicts a greater risk of storms in northern Europe in the second half of the century. What should we expect from these projections?
The IPCC indicates that the risk of storm could increase in Northern Europe with a fairly low confidence index. Generally speaking, the number of storms in France does not increase, it fluctuates. When we talk about climate change, the rise in temperatures is fairly scientifically consensual. The consequences on precipitation are less understood and France is located in an uncertain zone. We only know that we are heading towards more rain in northern Europe. For phenomena linked to wind, the projection is more delicate.