A vast low pressure system is organized from the Iberian Peninsula to the North Sea with a general flow from south to southwest unstable over France. A weather situation conducive to thunderstorms develops between Tuesday and Thursday, mainly affecting the southern and central part of the country. On the Gulf of Lion, the south-easterly wind blows up a mass of humid air towards the Cévennes where heavy stormy rains occur.

This Tuesday at 12 noon, violent thunderstorms have been breaking out since this morning in eastern Languedoc, and in particular between Hérault and Gard. 240 mm of water fell in Vacquières (34), 188 mm in Saint-Dionisy, 151 mm in Quissac (30) and 57 mm in Nîmes (30), which corresponds to 2 weeks to 1 and a half months of precipitation. . Floods are in progress between Nîmes and Montpellier. At 9 a.m., in a very unstable southerly flow, heavy stormy rains go up from the Mediterranean towards Languedoc and the Cévennes which suffer from occasional intense rains in a short time. Thus, between 7 and 8:30 am 107 mm of rain fell in Vacquières (34), 42 mm in Moulès-et-Baucels (34), 40 mm in La Grand Combe (30), 30 mm in Saint Hippolyte-du-Fort (30), which corresponds to between 2 weeks and 1 month of rainfall in the municipalities mentioned.

This afternoon, continuous precipitation of occasional high intensity continues until 3 p.m. in Languedoc and the Cévennes, with intensities of 5 to 8 mm / h, before weakening. On the other hand, at the end of the day, instability increases on the plains of the south-west and heavy thunderstorms rise from Haute-Garonne and Lot-et-Garonne towards Périgord and Limousin then the southern part of the Center. -Val de Loire to Burgundy. The thunderstorms are accompanied by intense rains, locally hail and strong gusts of wind.On the night of Tuesday to Wednesday, a temporary lull occurs in the Cévennes while thunderstorms continue to circulate from the southwest to the regions of the center where they are sometimes strong. On Wednesday, a new deterioration occurs in Languedoc and the Cévennes with heavy rains sometimes taking on a stormy character. The foothills of the Cévennes are the most exposed to strong intensities of rain between the north of the Hérault and Gard and the Ardèche Cévennes. In addition, the weather remains very unstable between New Aquitaine, the north-west of Auvergne and the south of the Center-Val de Loire region with new stormy showers. late night and early morning in Languedoc and Cévennes will shift towards the PACA region. If a few thunderstorms still affect the plains of the south-west, they will lose intensity with a tendency to gradually calm. Here are the characteristics of this rain-thunderstorm episode:
– significant amounts of rain in the Cévennes (100 to 250 mm)
– a risk of low-level flooding and flooding at the foot of the Cévennes.
– cumulative rainfall of 40 to 80 mm under the most active cells in the southwest, or the equivalent of 15 days to a month of rain.
– a risk of hail and gusts of wind to 80 km / h under the most violent thunderstorms in the southwest.

In a context marked by unstable weather since the beginning of this summer, thunderstorms will again mark the week in the south of France. They promise to be strong from time to time. This situation will lead our services to issue alerts on Monday evening.

After a summer weekend, this week is marked by a change of weather. Indeed, the high pressures are withdrawing towards the north of Europe, jostled by a cold Portuguese drop. This cold drop arriving in a mass of hot air, it will bring increasingly unstable weather with stormy degradation over a large part of southern France.

This Monday, September 13, the wind is moving to the south and the heat already present on the southern half on Sunday goes back to the north. In the afternoon, the atmosphere becomes muggy in the southwest with the weather turning to thunderstorm at the end of the day.

Related title :
Episode of heavy rains and violent thunderstorms
Weather forecast for Tuesday, September 14: return of thunderstorms in a heavy atmosphere
Weather Wednesday 15 September: very unstable weather, sometimes strong thunderstorms
Weather forecast for Tuesday September 14th: the return of thunderstorms
14 to 16/09: warning for heavy stormy rains in Languedoc and thunderstorms from the South-West in the center of the country

Ref: https://actualite.lachainemeteo.com