“In Mulhouse, we haven’t seen this since 1988”: why is there so much fog this fall in France?

The sun has been discreet in recent weeks in most regions of France. The fog has settled in and doesn't seem to want to leave. In Brittany, Vienne and Haut-Rhin, many Internet users share images of foggy landscapes on social networks. In Paris, the top of the Eiffel Tower is hidden, much to the dismay of tourists. Only the south of France is spared.

Is this phenomenon really exceptional? Yes, says Tristan Amm, forecaster at Météo-France (new window) interviewed by TF1info. He takes the example of Basel-Mulhouse where “the weather station recorded 15 days of fog in October, so every other day. And it continues in November, with already four days of fog. You have to go back to 1988 to observe such an occurrence!” The average in recent years is closer to eight days of fog in October.

Another example: in Strasbourg (new window)Météo-France recorded ten days of fog in one month. This means visibility has been less than a kilometer two to three days a week.

A phenomenon difficult to anticipate

“The north of France and the Siena valley, in the English Channel, are particularly concerned”confirms this expert. In question, favorable conditions: “You should know that fog is simply a cloud that stays at ground level. The atmosphere is very humid, there is a lot of water in the air and we observe cooling at ground level.” After this “dew point”, the carbonated water then transforms into small droplets, which remain stuck in suspension. The fog remains stuck these last few days because “the weather is calm, thanks to the anticyclones” currently positioned in Western Europe, explains Tristan Amm.

If autumn is the most favorable season for “fog” each year, nothing says that it will disappear with the arrival of winter. “It is not uncommon to see fog all day in December and January”admits the forecaster. Note that this phenomenon absolutely does not portend a very cold winter, or on the contrary a particularly mild one, and that it remains very difficult for meteorologists to anticipate, “even overnight”.

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If fog is therefore a natural phenomenon, it constitutes a real danger for motorists, because of the lack of visibility. According to Road Safety figures, “Accidents in foggy weather are twice as serious as in normal weather”.