The Caetano storm which affects France with wind And snowfall also causes strong temperature contrasts. This Thursday, it is possible to have around ten degrees of difference in just a few kilometers.
“The air mass remains cold on the northern flank of the Caetano depression,” notes Keraunosthe French observatory for tornadoes and violent storms. It particularly focuses on the situation in Brittany.
At 11 a.m., the difference could even reach 13°C. The Weather Channel thus reports 15°C in Nantes (Loire-Atlantique) when at the same time it was only 2°C in Rennes (Ille-et-Vilaine). About a hundred kilometers separate the two cities.
The temperature contrast is incredible in the northwest! It was 15°C in Nantes compared to 2°C in Rennes at 11 a.m. There will be very little development in the afternoon. pic.twitter.com/OprdYgUUIA
— La Chaîne Météo (@lachainemeteo) November 21, 2024
The situation was similar at the start of the afternoon between Nantes and Angers (Maine-et-Loire). It was 12°C in the first compared to 3°C in the second while a little less than 80 km separate the two cities.
The confrontation between these two air masses
But the distance with such or almost such a temperature difference can be even more remarkable. A little after 1 p.m., this was the case in Indre. 3°C was measured in Neuillay-les-Bois compared to 13°C in Saint-Gaultier. The two weather stations are located around a hundred meters above sea level. They are only separated by… 15 km, as shown in this map provided by Weather sky where the two localities have been circled in red.
This situation is explained by the circulation of air masses which cause the snowfall this Thursday. A descent of dry polar air has occurred since Wednesday in the north of France. At the same time, a significantly warmer and more humid air mass rises along the Iberian Peninsula.
It is the meeting and confrontation between these two air masses which are at the origin of snow. The flakes fall north of the demarcation zone. This zone is very narrow, which is reflected on the ground and is the cause of these sudden temperature differences over short distances.