After the peak of heat which affected a large part of the country at the start of the week, the first real coolness of the meteorological autumn is in sight for the weekend. A descent of polar air will occur over our country. Large variations in temperature are a usual phenomenon in September, but, after a long-lasting hot summer, it may come as a surprise to find temperature levels that we had not experienced since last spring.
After the monthly heat records broken on Monday in the southwest with locally up to 40°C in the shade, temperatures will eventually drop significantly in the second half of the week. The weekend will be marked by freshness and we will have lost in some regions up to 15°C in the space of a few days.
Credit: The Weather Channel
Establishment of a northerly flow causing temperatures to drop from Thursday
From Monday to Wednesday, France is under the influence of a vast low pressure system which extends from Portugal to the Bay of Biscay. The general flow is oriented towards the south and brings up very hot air from North Africa. Monday was the hottest day but the temperatures, although slightly down, will remain well above normal for the season until Wednesday. Note that a high heat peak occurred at the same time only 2 years ago with 37.8°C on September 14, 2020 in Dax.
From Thursday, an anticyclone will reinflate over the British Isles while a depression will form between Scandinavia and Central Europe. Between these two systems, a northerly flow will take place over France and significantly lower temperatures. It will be a polar air descent. The decline will begin on Thursday in the northern half before generalizing to the whole country on Friday. The next weekend will be cool with temperatures no longer exceeding 15 to 19°C in the afternoon over a large northern half and 20 to 27°C in the southern part of the country. We will then be 3 to 4°C below the average for the season. The feeling will be very fresh exposed to the northeast wind. In the Mediterranean, the mistral and tramontana will blow hard, as will the westerly wind over Corsica.