What causes this persistent fog?
Steven Tual : “Since the end of October 2023, a little before storm Ciaran, we have experienced a very long period of depression, which explains the lack of sunshine this summer in particular. There, for the first time in a year, an anticyclonic period set in, with high pressures, extending from the Azores to central Europe. With all the rain that has fallen and the humidity accumulated on the ground over the past year, combined with the fact that there is little wind, we find ourselves with so-called advection fog: clouds 100 to 300 m thick which are pressed to the ground by the anticyclone and form this persistent grayness. Thus, in Saint-Brieuc, we have just gone four days without the slightest clearing – or even five days, because there were only 9 minutes of sunshine on October 30. »
“Yes, sometimes sunny spells sneak in and immediately warm the air, giving a spring, almost summer atmosphere. This is the case in Saint-Brieuc and Sud-Goëlo at the moment. It is not impossible that the gray will return in the afternoon. But if the sun continues, it will be hot: thus, yesterday, Monday November 4, it was 18.8° in Plusquellec, near Callac, while it was only 10.8° in Saint-Ygneuc (Jugon -the-Lakes). Above the low clouds, the air mass located around 1,500 m altitude is exceptionally warm for the season, around 10 to 12 degrees. If we had mountains in Brittany, it would be beautiful at altitude. This has also been the case on the Monts d'Arrée in recent days; and yesterday, on the heights of Lanfains, we recorded 16.5° while it was 11.3° in Pordic. »
Your predictions for the coming days?
“For meteorologists, it is very difficult to know when a ray of sunlight will succeed in piercing these clouds in this or that place, on this or that day. Perhaps we will have small clearings on Saturday or Sunday, because disturbances could bring a little wind. But overall, the anticyclonic conditions which are the cause of this fog will persist at least until November 10, and probably even longer. So we're going to keep this low gray with the sun above. This is also why November is really the month of seasonal depressions, of the negative impact of the weather on people's morale: because with an anticyclone, we have gray weather; and if we had a depression, it would be rain and wind…”
