Weather Alert: Bad weather: thunderstorms, strong winds and Cévennes episode

From Saturday April 27 at 12:00 to Tuesday April 30 at 12:00.

Situation

– this Saturday, violent storms, sometimes severe, break out from Aquitaine to the Loire Valley and Normandy. This stormy wave will be violent, but brief, ending in the evening.
– this Saturday, southeasterly winds are blowing strongly in Languedoc and the south of the Massif-Central, as well as in the mountains with a storm at altitude and strong waves on the coast.
– tomorrow Sunday, the improvement is clear in the west and the winds weaken in the south-east. But, the rainy-stormy episode takes place over the long term on a not very mobile and stationary axis going from the Gulf of Lion to the Cévennes and going up to the center-east. These heavy rains will take on a marked stormy character over the Hérault.

By the persistence of this rain until at least Tuesday evening in these same regions, the accumulations will become very abundant (exceeding 200 to 250 mm locally), and we can now fear significant flooding in the Cévennes and southern Massif watersheds. central at the start of the week.

Observation

This Saturday

At 3 p.m., the situation quickly deteriorated with the multiplication and strengthening of storms between Aquitaine and Pays de la Loire. The wind strengthens in the Massif Central and blows at nearly 100 km/h between Le Puy, Millau, Mende and above Saint-Etienne.

At 12, the disturbance linked to the depression rises along the Atlantic regions as far as the Perche, causing sustained rains, without any aggravating character for the moment

At 9 a.m., the depression responsible for the bad weather is located on the Bay of Biscay and is beginning to rise towards the Atlantic coast. Ahead of this depression, showers occur in the southwest and take on a stormy character when reaching the Pays de la Loire.

Evolution

Chronology and characteristics of this degradation

This afternoon
The stormy deterioration sets in in the afternoon, between the Pyrenees, Aquitaine, Limousin, and all of west-central France. The strongest storms break out between the Garonne and Limousin at the end of the afternoon, with hail and powerful wind gusts of up to 100 km/h. In the Loire Valley, rainfall amounts are expected to be significant. In the evening, these storms reach as far as Normandy, also affecting, to a lesser extent, Ile-de-France. The lull will be quite rapid after 10 p.m. Accumulated rain could reach 40 to 50 mm under the strongest storms, which could lead to heavy runoff and occasional flooding.

At the same time, southeasterly winds are clearly strengthening between the Gulf of Lion, the south of the Massif Central and the Rhône valley (gusts between 80 and 100 km/h in plains and valleys, and 120 km/h in the mountains) .

Tonight and tonight
The storms are calming down, but still heavy showers persist in the central regions and Normandy.
To the south-east, the winds blow strongly around the Gulf of Lion and the Massif Central, as well as in the Rhône valley and the Pre-Alps (up to 100 km/h on the plains). At altitude, a Foehn storm is expected (gusts reaching 130 km/h).

Tomorrow Sunday
The weather becomes calm again in the west. To the south, the wind weakens significantly. But the rains will continue all day from the Gulf of Lion to the Cévennes and the center-east. They will be regular, with temporary intensifications, particularly in the morning, then at midday and especially at the end of the afternoon, when violent storms will break out in Hérault and Gard. Some of the largest accumulations are even expected on the Hérault plain, and not only in the mountains as is often the case. The risk of flooding will therefore be increasing both in areas of relief, but also in the plains under stationary storms (“V” storms, taking the shape of this letter on satellite images). risk seems to be Sunday evening.

Further trend
The rainy episode will persist overnight from Sunday to Monday in the same regions, temporarily losing a little intensity.

List of departments concerned