A classic breath of fresh air for September?
This sudden arrival of autumn is nothing exceptional. In fact, it is usually in mid-September that the first cold snaps occur in France. Don’t go back very far (September 2022) to find traces of a cool and unstable mid-September with the first frosts in the plains on the 18th.
But, a marked breath of fresh air
Indeed, our thermal indicator indicates that the temperature deficit on a national scale will reach 3 to 6°C between Wednesday and next Sunday.
National thermal indicator from September 9 to 17 © the weather channel
Temperatures close to All Saints’ Day!
The lowest point of this cool episode will be reached next Thursday for maximum temperatures. The average maximum will be 15°C across France. The 20°C will barely be reached near the Mediterranean. With a maximum of 13°C in Lille and Strasbourg, 14°C in Paris, Lyon and Orléans and 16°C in Bordeaux, temperatures will be 4 to 7°C below normal, at the level of late October.
Very cool next Thursday © the weather channel
Polar dropout in question
This great freshness is linked to the plunge of a polar air mass that will descend to the Mediterranean while passing through France. At altitude, around 1500 meters, the temperature of the air mass above France will be around 0 to 3°C.
Polar air plunge over France this week © the weather channel
A whole week of refreshing mistral and tramontane winds in the Mediterranean
Due to the deepening of a depression over the Gulf of Genoa, dominated by cold air on a warm sea, a lasting period of mistral and tramontane winds will set in from Monday. This wind will continue until next Saturday. It is therefore a whole week of strong winds that will affect the shores of the Mediterranean.
Mistral and tramontane present all week in the Mediterranean © the weather channel
Snow in the mountains
As this polar air mass will be maritime, it will generate rain and showers. In the mountains, the first snowfalls of this end of summer are expected in the Alps and the Pyrenees from 1800 meters on Thursday. The highest peaks of the Massif Central could also turn white.
Risk of snow in the mountains © Between Wednesday and Friday
Towards very cool mornings at the end of the week and white frosts
From Thursday evening, the clearings should return, which will help the temperatures to drop. The nighttime coolness will increase in the following nights, especially during the night from Friday to Saturday. The presence of cold polar air at altitude and the clear night sky will accentuate the radiation, especially since the length of the night is now increasing very quickly. As a result, the first white frosts could appear in the plains on this occasion, between the interior of Normandy, Sologne and Limousin.
Marked morning freshness next Saturday © the weather channel
