Weather alert: intense rains, thunderstorms and wind from the center-east to south-east – La Chaîne Météo

From Sunday October 3 at 5:00 p.m. to Monday October 4 at 6:00 p.m.

Situation

A very important low pressure system stretches from the British Isles to France with warm air coming up from the Mediterranean and conflicting with much cooler air coming from the Atlantic. France is at the heart of this conflict of air masses, with the slow progression of a very active disturbance. This disturbance now affects the central-eastern and south-eastern regions which are subject to bad weather, in the form of a Cevennes episode, intense rains and violent thunderstorms. These bad weather continued until Monday evening from Provence Alpes Côte d’Azur to the Cévennes.

Observation

This Sunday

At 9 p.m., the pluvio-thunderstorm disturbance remains active from the center-east to the south-east. After having swept the lower valley of the Rhône and the Camargue and brought significant accumulations of rain in a short time (up to 87 mm of water in Uzès, 71 mm in Tarascon and 46 mm in Nîmes between 6 and 8 p.m. this evening), the strongest thunderstorms reach Provence, Drôme and Vaucluse. In the Cévennes, it is very temporary lull. Finally in Rhône-Alpes to Burgundy and Jura, long-lasting rains occur, with moderate intensities of 3 to 7 mm / h.

At 18 o’clock, very intense and stationary rains still occur in the Cévennes where the accumulations become impressive. We recorded 452 mm in 24 hours in Villefort (Lozère), 379 mm in Concoules (Gard). In Lozère, the 6-hour rain record dating from September 2014 (250 mm) was broken with 253.6 mm. For Villefort station (Lozère), the all-month precipitation record of 428 mm (01/11/2008) has already been broken. Significant floods occur on the rivers descending from the Cévennes such as the Gard to Mialet which has just exceeded the reference flood of October 11, 2014 (5.08 m) with 5.15 m at 5:50 p.m.!

At 15h, the Cevennes episode continues, with increased rains. Since Sunday 00 h 316 mm of rain fell in Villefort (48), which corresponds to 2 months of rain in this city. River floods are observed, especially along the Cèze, a tributary of the Rhône. The southerly wind tends to weaken between the Grand Est and Rhône-Alpes and no longer exceeds 80 km / h, except in the mountains where it remains turbulent.

At 12 , intense rains persist on the Cévennes heights with more than 200 mm recorded in the east of Lozère since midnight. The wind is blowing very hard in the Grand Est with gusts reaching 100 km / h at Mathaux-Etape (10) and 90 km / h at Nancy (57). The wind is blowing less strongly in Auvergne-Rhône-Alpes than this morning with still 70 to 80 km / h of wind between Lyon (69) and Mâcon (71).

At 9 o’clock, as expected, the cold front is finally shifting further to the east, straightening up. This is the end of monitoring for the northwestern departments even if it continues to rain steadily until late morning but without any real direct consequences. On the other hand, degradation is well in place in the Cévennes with sometimes dilluvian rains and hourly intensities sometimes exceeding 100 mm. The southerly wind blows violently on the center-east with gusts to 70 km / h in Saint-Etienne and up to 112 km / h in Sauvages (Rhône) which has also recorded a maximum gust of 130 km / h last night.

At 7, the cold front continues to undulate over the same regions of the Pays de la Loire to the Paris basin and to Normandy with still heavy rains. Hourly intensities sometimes reach 15 mm / h as in Sarthe at Luart. It fell over the last 24 hours up to 98.9 mm at Nantes Villes and 93.1 mm at the Nantes station, which makes it a monthly record for the station, the previous record dating from 1979. At the front from the cold front, on the eastern facade, the southerly wind blows violently on the center-east with gusts between 70 and 80 km / h. Heavy precipitation also developed in the Cévennes with hourly intensities between 15 and 30 mm.

Evolution

Here is the chronology of this important and lasting episode of bad weather

Tonight, the heaviest stormy rains occur in the PACA region and to a lesser extent in Drôme and Isère. Under the most intense rains, significant runoff occurs which can cause mudslides, floods and floods. In the Cévennes after the episode of torrential rains in the afternoon of Sunday, more moderate rains are back tonight.

On Monday, this agitated weather is maintained from Languedoc to the Cévennes to the middle valley of the Rhône. It also concerns the Provence Alpes Côte d’Azur region where several stormy episodes sweep the region during the day, which can cause hailstorms, intense rains in a short time and gusts of wind to nearly 100 km / h C It is only late in the evening, after 9 p.m. that conditions will improve in the southeast with the disturbance evacuating to Italy.

During this bad weather episode we wait

– violent winds, up to 100 km / h on the reliefs of the Massif Central, in the Val de Saône, in Lorraine and in Champagne, which can cause trees to fall on the roadways and electric cables.
– heavy rains, with very significant accumulations of up to 50 to 100 mm in 24 hours, up to nearly 400 mm in the Cévennes by Monday evening.
– strong thunderstorms in Provence Côte d’Azur with a risk of hailstorms
– a high risk of urban runoff, floods and flooding in the sectors most exposed to heavy rains and stationary storms.

List of departments concerned