After the great freshness of this week, accompanied by a good sun, a new drop in polar air will sweep France from Monday. Temperatures will drop to 5°C below average. It will be a truly autumnal time with the return of the good rains, sleet accompanied by a constant wind as well as the appearance of snow on our massifs from 1400m above sea level. The arrival of autumn is therefore sensational, but it corresponds to the calendar.
Therefore, autumn is at the rendezvous in France and, in general, in north-western Europe. Thus, after the wave of dry freshness this week, a new drop in polar air coming directly from Iceland will sweep our country at the beginning of next week. Unlike the last few days, in which we have been affected by calm and anticyclonic weather characterized by large thermal amplitudes between morning and afternoon, this time it will be cold with low pressure, accompanied by wind and frequent showers. In the mountains, the snow will fall from 1,400 to 1,500 m.
A descent of polar air of maritime origin
This descent of cold air from Iceland will be channeled by the presence of a depression that will circulate over the British Isles. The wind will turn to the northwest sector over France, bringing fresh and moist air of maritime origin. This is therefore a very different configuration to the one we just experienced where the colder, drier air mass came from northern Norway.
Next week will therefore be characterized by the return of unstable, cool and windy weather. The sensation will be very different from the beautiful days of this week, since if the nights will be less cold thanks to the clouds and the wind that will limit the phenomenon of nocturnal radiation, the afternoons will instead be cooler due to the wind, the showers and many clouds. The atmosphere will be truly autumnal, with temperatures at a mid-October level. At altitude, this will result in a cold and gloomy climate, with frequent snowfalls from 1,400 to 1,500 m altitude. Our beds will turn white, around the same date as last year (September 20, 2021).
It should be noted, however, that this air mass will fly over the North Atlantic and the British Isles before reaching France: it will therefore be smoothed out relative to its origin, which is characteristic of oceanic air masses. The fact is that average temperatures in France will drop about 4°C below normal for the season next Tuesday, which will be the coolest day.
Finally, significant rain accumulations!
The good news for some is that the rains will reach our country quite widely, after which they will have already fallen this weekend. Starting Monday afternoon, the British Isles riots will parade across our country, from north to south. The southeast quarter will be windy with the mistral and tramontane, but we do not expect new accumulations of rain after the storms of the weekend. On the other hand, the parade of rains and showers will bring water to almost the entire territory.
However, the accumulated rains over the next week will be quite uneven, but more abundant due to a blocking effect on the western and northwestern slopes of the mountainous regions. Accumulations of 40 to 80 mm have been recorded at the foot of the Pyrenees, in the Central-East and East regions, as well as near the coast of La Mancha. In the mountains, we can exceed 80mm, and probably more towards Franche-Comté. Elsewhere, the plains, particularly the central regions that are still dry, could see 10-30mm from the succession of disturbances.
Lots of snow in the mountains
The parade of riots, combined with the drop in temperatures, will generate frequent snowfall from Monday night from 1,400 to 1,500 m above sea level, then especially Tuesday and Wednesday, particularly in the eastern reliefs. The Vosges ridges could also be whitened. For the Pyrenees, the rain-snow limit will be greater, between 1,800 and 2,200 m depending on the massifs. In the Northern Alps, the most exposed, we could accumulate 30 to 50 cm of fresh snow at 2,000 m in our highest stations, and more than 1.50 m at 3,000 m altitude.