We know that the coming week will be very unsettled, and that a cooling will occur. Indeed, a vast low pressure system shifts in Scandinavia and an anticyclonic blockage in Greenland forces the flow to take a northwest component. The trend is therefore reliable.
On the other hand, sensitive weather will be driven by secondary depressions which are poorly understood by the models. Their potential trajectories can greatly affect the weather at a given point. The more depression evolves over time, the more uncertainty increases..
This is a manifestation of what is known as the “butterfly effect” where a small difference can lead to much larger changes.
Illustration of the uncertainty in the middle of next week. The main depression is large and well established. Secondary depression adopts a chaotic, unpredictable trajectory – WXCharts / MeteoVilles
In meteorologist jargon, we say that the models are “floundering”. They are constantly changing, not for the big picture but in its fine-tuning. Both storm and snow phenomena are located under a secondary depression, and strongly depend on the trajectory of the latter. Thus, the slightest initial change has major consequences on the final time in France: Snow/rain, cold/mildness, calm/storm
To illustrate it, let's take two models from this Sunday morning : GFS (American) for the 6h run and CEP (European) for the 0h run. The forecast was therefore generated using similar parameters!
American model (GFS 6z) – The secondary depression circulates on an axis going from northern Brittany to Lorraine via Île de France. The mildness goes back very far to the North as well, rejecting the snow near the northeast borderson the borders of the country.
Weather situation for Thursday, November 21 at 1 p.m. – GFS 6z of November 17, 2024 weather sky
European model (CEP 0z) – The secondary depression circulates on an axis going from Bordeaux to Corsica via the Gulf of Lion. The mildness is pushed far to the South, as is the band of strong winds and the associated rains. The snow reaches… Avignon, Nîmes, and even the Côte d'Azur!
Weather situation for Thursday, November 21 at 1 p.m./4 p.m. – CEP 0z November 17, 2024 weather forecast
France will be at the heart of the disrupted flow: On a large scale, the vast Scandinavian low pressure area will direct a disturbed flow over the country. Precipitation will therefore be abundant under the various disturbances (still across the country). Episodes of strong winds are to be expected.
Precipitation and position of action centers during the coming week – GFS 12z Tropicaltidbits
Heavy rains
Rains will be frequent and abundant across the country, the conflict zone will be the wettest, as will probably the mountain ranges (Alps in the lead) due to the barrier effect.
Precipitation accumulation during the coming week – GFS 12z / WXCharts
Significant thermal contrast
The temperature contrasts will be significant: A conflict between cold air of polar origin and mild air of subtropical origin will take place, if the areas of conflict are unclear, these conflicts will occur in our country or nearby. It will be more likely to be on the cold side going towards the North-East, and vice versa when going towards the South-West.
Temperature anomalies at 1500m during the coming week – GFS 12z / TropicalTidbits
The risk of storm
The winds will be strong: Due to these significant contrasts and strong dynamics, strong winds are expected to affect the country. Generally speaking, we can expect up to 100km/h and locally more on the coasts, and more than 60km/h elsewhere. The southern half of the country seems more exposed inland.
Heaviest gusts expected during the coming week – WXCharts
The risk of snowfall in the plains
Snow should fall at low altitude, or even in the plains: If the exact location is impossible to know currently as we saw above, the chances will increase significantly heading towards the North-East. They will weaken as they go towards the South-West, becoming almost zero in Aquitaine.
Probability of snowfall in France for Thursday November 21, 2024 – WXCharts
