The phenomenon is quite exceptional at this date. It snowed on Wednesday evening in Brest and its surroundings, in the Finistère department. This phenomenon is linked to the bad weather currently affecting the west and north of France.
It is already quite rare, even if it is not at all a new phenomenon, for flakes to fall by the sea or ocean because the immediate proximity of the body of water tends to warm the atmosphere. Where the situation is more remarkable is that the snow shower occurred on March 27, when spring had begun. Météo France mentions several events in the region, but generally in winter. In 2010, it fell about fifteen centimeters in December.
A little after 8 p.m. on Thursday, the temperature dropped low enough for the rain to turn into snow.
Before the strong winds this Thursday, the snow made a notable return to Brest (Finistère). 0.6°C on the thermometer at the Météo France station around 8:24 p.m. #Brittany #Brest #snow https://t.co/fOSFNOcCLF
— Kévin Floury (@kevinfloury) March 27, 2024
Even though it was loaded with moisture, it was able to hold on to the ground in places in the region.
❄️ The snow locally left a small layer on the ground in the north of Finistère this evening of March 27, here from the commune of La Martyre. (© Jean Baptiste Colliot) pic.twitter.com/UECs7F4O5j
— Météo Express (@MeteoExpress) March 27, 2024
Inland, near the Monts d'Arrée, in Landivisiau, the snow shower was also quite remarkable.
❄️ North Finistère under the snow this March 27! Images of Landivisiau where the temperature dropped from 11°C this afternoon to 0°C this evening! (© JulienBzhh) pic.twitter.com/RQdCf5KChS
— Météo Express (@MeteoExpress) March 27, 2024
The reason for the unexpected occurrence of these flakes lies in isothermal conditions. This is an area where the temperature remains the same. Concretely, this means that the temperature was low and stable enough between a high enough altitude and the ground so that the snowflakes did not turn into rain. The temperature in Brest on Thursday was around ten degrees shortly before.
Such a situation occurs when precipitation is heavy and wind is weak. To summarize, on the path from the cloud to the ground, precipitation increasingly cools the air. In yesterday's case, the high altitude flakes eventually cooled the air at lower and lower altitudes until they reached the ground, ending the rain and replacing it with snow. In this case it is generally very humid.