What conditions exist in Toulouse for it to be submerged under a sheet of fog?

This is a common phenomenon, but not frequent. Since this morning, the Pink City has been immersed in a sheet of fog which, over the hours, tends to dissipate. Mist already present yesterday, especially in the evening, and which should be present again this Tuesday morning. “It’s the fog season, there is frequent fog between the months of November and January. It evolves over the hours and in Toulouse tends to dissipate thanks to the presence of the Autan wind,” recalls Patrick Galois , forecaster at Météo France.

However, this Monday, no gusts came to disperse the fog. And it tends to persist when there is little thermal amplitude during the day, with differences in degrees that fluctuate little between the evening and the morning. This Monday, it was 3°C at 1 p.m., 2°C is announced at 7 p.m. and 0°C at 1 a.m. but also at 7 a.m. this Tuesday.

“We are dealing with radiation fogs. This happens when the nights are longer and longer, the earth cools, the atmosphere too, and the humidity level is at its maximum,” continues the specialist.

The humidity can no longer escape, it is somehow trapped in a cloud of water droplets as close as possible to the ground. The sun is not high enough, and not strong enough to pierce the cloud layers, the fog becomes thick, to be cut with a knife as the saying goes. “All valleys, including that of the Garonne, favor the formation of fog. The water provides a source of humidity and there is a basin effect with the cold air which remains at the bottom of the valley. But it is a phenomenon that we find more often in Agen than in Toulouse where the Autan wind often plays a dissipating role”, concludes Patrick Galois.

If we know that certain areas are more conducive to the formation of fog, such as valleys, marshy areas or even forest areas, it is difficult for meteorologists to predict their duration or even their intensity, due to the complexity in their training process.