Be careful on the roads. The north of France is exposed to ice, or even a few flakes, for the start of the weekend.
This Friday, Météo France is placing a large northern part of the country on yellow alert (level 2 out of 4) for this reason. In the Massif Central, Lozère is also affected.
Apart from this department, no precipitation is expected this Friday in the vigilant departments. But three factors must be taken into account. Firstly, temperatures will remain close to 0 all day, or even fail to cross this bar and remain in the negative. “The thaw is difficult” in Lorraine in particular, insists Météo France. “From the English Channel to the North-East, thanks to the drop in temperatures, patches of ice” have formed. Additionally, with low temperatures and high humidity, precipitation over the past few days may have had difficulty drying out. With frost, this can lead to the formation of black ice.
Finally, a third point is favorable to road freezing: the relative humidity is close to saturation. This indicator corresponds to the ratio between the water vapor present in the air and the maximum possible quantity. At a level of 100%, it is saturation with a risk of fog, dew or frost. In the departments on alert, the rate of 100% is often reached or close to being reached this Friday. With temperatures near 0 or below, these are conditions conducive to freezing fogs whose droplets freeze upon hitting the ground.
On Saturday, the same area as that affected this Friday will be at risk of icy conditions, but in much worse conditions. Rain will arrive from the west and southwest of the country, accompanied by a sharp rise in temperatures in the process. This conflict between a cool air mass and a warmer, humid mass will be favorable to the formation of snow and ice at the start of precipitation.
The period most at risk will be the end of the day and the evening, when many motorists are likely to return from vacation. In theory, it is near the borders that the risk will be highest. But a variation of one or two degrees can have a big impact on the affected area.
“The rain should arrive at the beginning of the afternoon in the Paris Basin, and north of the Seine during the afternoon. The temperature level will determine the onset of snow and the formation of ice. Everything will also depend on the chronology of the movement of the disturbance,” explains The Weather Channel. “This episode would be short-lived (1 to 3 hours), replaced by the general mild spell during the night from Saturday to Sunday. »