Temperatures 5°C below seasonal averages, snow on the highlands and chilly winds in the Mediterranean… From Monday to Saturday, the weather will deteriorate with temperatures similar to those of All Saints’ Day.
Without transition, autumn, normally expected on September 22, has returned a little early this week. And this, almost everywhere in France. On the program: gray skies, rain, wind and particularly cool temperatures. In its forecasts, Meteo-France estimates that Friday September 13 will be the coolest day with temperatures 5°C below seasonal averages, snow in the mountains and possible first frosts… In other words, All Saints’ Day weather. The fault of a “maritime polar air mass”.
The expression leaves a chilling impression. But, next to LiberationOlivier Proust, forecaster at Météo France defuses: “This is an expression that should not be taken literally, it is meteorologist jargon.” Concretely, it designates an air mass “who comes from more northern latitudes, from the polar circleand who has a maritime background”.
As it travels, this air mass evolves. “It crosses a less polar environment, becomes humid over the oceans and becomes milder”continues the specialist. So much so that in the eyes of a meteorologist, the expression refers above all to a cool air mass “in the lower layer”humid and favouring showers.
The consequence for the French? Very gloomy weather. “Throughout the week, we will see a succession of rainy spells followed by showers, systematically accompanied by a moderate but fairly strong northwest wind.”
This Thursday, temperatures have already plummeted. 6°C this morning in Strasbourg and Clermont-Ferrand, 7°C in Lille, 10°C in Bordeaux… It will also be barely more than 20°C during the day in the Mediterranean, where “a fairly long sequence of winds (mistral, tramontane)” is planned, specifies Olivier Proust.
“Quite rare at this time of year”
“The expected morning freshness is quite rare at this time of year”observes the forecaster. Before adding: “At daybreak, we will have temperatures around 8°C. If we look at recent climatology, that doesn’t happen often before September 15th.”. The previous two? Once “recently”in 2019. And another one… in 2001.
However, the expert is more optimistic for the end of the weekend where, according to him,“the westerly winds will take over and bring milder temperatures”.
Another remarkable fact of this chilly sequence: «Snow expected at 1,500 meters in the Alps and 1,800 meters in the Pyrenees”underlines Olivier Proust. The crests of the Jura and Vosges could experience their first “sprinkling”. What is “quite early”the expert breathes. Last similar episode: September 2020, when snow fell in abundance above 2,000 meters in the Pyrenees and the Alps, Météo France recalls on its website.
Cautiously, the meteorological agency specifies that the drop in temperatures this season “is not incompatible with the context of climate change”. According to her, it is completely normal to observe a “variability” of our climate from one year to the next. And, thus, to experience cooler periods at any time of the year. However, she concludes, “these events are becoming rarer and less intense than before”.
Updated Thursday, September 12: new temperatures.
