It’s confirmed. The snow will fall on the plain Thursday in several regions of northern France, according to the latest forecasts this Wednesday morning. It remains to be seen what will be intensity and precise locationuncertainty remaining particularly for Île-de-France.
France is facing a descent of polar air which is causing a sharp cooling of temperatures this Wednesday. This mass of cold air, with temperatures close to -35°C at 5000 m altitude depending on Keraunosthe observatory for tornadoes and severe thunderstorms, will collide with a warmer and humid air mass coming from southern Europe, as shown in the map below. It is in the northern part of the meeting zone between these two opposing masses that snowfall will occur.
❄️A snowy episode should occur within an air mass conflict on Thursday, as a depression passes through.
The extent of the depression deepening is still poorly understood, with a snow axis still uncertain in latitude and overall models scattered across the… pic.twitter.com/57Qh4QLCpX
— Keraunos (@KeraunosObs) November 19, 2024
But being precise to within a hundred kilometers remains tricky. This distance is tiny on the atmospheric scale. This is why, despite the fact that snow showers are expected for Thursday from daybreak, it remains difficult to know if the flakes will fall in the regions which will be at the limit of the phenomenon, which is the case of Île-de-France.
“Snow is possible at very low altitude down to the plains over a good northern half of the territory, but there is still significant uncertainty both about the phenomenon and its intensity. The regions going from Lower Normandy, to the Pays de la Loire, via the Center and Burgundy to Franche-Comté currently seem to be the most targeted,” explains Weather France. In addition to the Alps, Jura and Vosges massifs, the organization is placing a large swath from Brittany to Burgundy on yellow alert (level 2 out of 3) due to snow and ice for Thursday. The Paris region is included in this vigilance map.
The progression of snowfall should be from the west to the east of the country. Brittany, Normandy and northern Pays de la Loire would be affected late at night and in the morning. The center and the Paris basin would be in the middle of the day and in the afternoon, the rest of the regions concerned in the afternoon and at the end of the day.
After a long hesitation in recent days, the different weather models now agree that all these regions will be affected at one time or another of the day. But they nuance the situation to the north and south of the main snow band.
The ECMWFthe European Center for Medium-Range Weather Forecasts, targets an area a little further north than Météo France’s vigilance map. According to him, Brittany would not be one of the most exposed areas, unlike Île-de-France.
Even within Météo France, a nuance can be felt. Its large-scale global model Arpeggiowhose map below covers the accumulations until the night of Thursday to Friday, is counting on the presence of snowflakes in the Paris region.
Conversely, the model Aroma is much more measured. More detailed than its global colleague, it analyzes localized phenomena and only anticipates, for its part, a possible sprinkling of the southern part of the capital region.
The result of this model is equivalent to that of the German model icon. The latter also anticipates that, massifs aside, the most affected regions will go from Brittany to Burgundy-Franche-Comté. The south of Île-de-France would be the only part of this region to be slightly affected. Icon was the first model to bet at the end of last weekend on a shift in snowfall in the West and in Brittany in particular, at a time when most ruled it out and still visualized snow showers in the North and the North-East.
Finally, the American model GFS cast a little wider net. It does not exclude snowflakes as far as the south and east of Hauts-de-France as well as in the northernmost parts of the Grand Est region. It is also counting on accumulations of up to ten centimeters in the Orne.
All of these weather models report raw precipitation values. They absolutely do not bode well for any ground hold. This depends both on the intensity but also on the temperature of the ground. The snow will hold more easily in the countryside than in the city where the difference in temperature on the ground can be very significant. As it stands, forecasts range from a dusting to around ten centimeters in the most exposed areas. Furthermore, the first scattered flakes could appear at the end of the day this Wednesday, in Seine-Maritime and Haute-Marne, in particular.
In any case, Météo France is already warning of a danger for Friday morning: refreezing. This is ground that freezes again after thawing. Temperatures and snow should favor this phenomenon in several regions. “In a context of possibly still snowy ground combined with cool temperatures, the risk of refreezing in the northern half is quite significant. »