Of
Monday October 7 at 4:00 p.m. au
Tuesday October 8 at 4:00 p.m.
Situation
A stormy rain disturbance crosses France this Monday and Tuesday from the Pyrenees to the eastern borders. It is very active, initially generating a risk of strong thunderstorms accompanied by hail from Aquitaine to Burgundy this Monday afternoon.
Then a Cévennes episode of high intensity but quite short also begins at the end of the afternoon and continues all night with heavy stormy rain and wind. These heavy rains and storms also reach Auvergne-Rhône-Alpes and Bourgogne-Franche-Comté as well as Provence Côte d’Azur.
This precipitation promises to be very intense between Languedoc and the Cévennes, over a “relatively short” duration not exceeding 24 hours.
Observation
This Monday evening and night
Heavy rains spread and affect many regions, initially from the Aquitaine basin to Burgundy where hailstorms are expected. Then, these precipitations will strengthen This evening in the Cévennes, Hérault and Gard due to a strong sea wind. This is therefore the start of a Cévennes and Mediterranean episode which will last 24 hourswhich remains quite short, but whose intensity will be significant.
Evolution
Tonight from Monday to Tuesday
This is the most risky period with the onset of the heavily rainy episode between the lower Rhône valley, the Cévennes, the Loire, the Rhône and the Jura. The strong storms will not only affect the mountains, but will also circulate in Lyon and the Val de Saône.
Heavy stormy rain accompanied by strong wind (100 km/h) will fall all night Monday to Tuesday from the Cévennes to Franche-Comté and south of the Alps to Isère via Lyon. The entire Rhone corridor will then experience very degraded weather conditions.
Bordering departments will also be affected, in the PACA region, Auvergne-Rhône-Alpes and Franche-Comté, but to a lesser extent. Roussillon will once again be less copiously watered, because the flow will not be oriented enough to the east for the rains to linger there.
Tuesday morning:
The weather will remain very rainy and stormy from the Rhone corridor to PACA, to the Alps and Franche-Comté. In these central-eastern regions, given previous rainy episodes and saturated soils, hydrological reactions could be significant. Strong thunderstorms will also circulate over Provence Côte d’Azur accompanied by fairly strong easterly winds.
At the start of the morning (8 a.m. to 11 a.m.), a virulent line of storms is forecast to sweep east of Bouches-du-Rhône, part of Vaucluse, then head towards the Alpes-Maritimes where it will be blocked for a longer period of time. Thus, despite the sudden intensity, the accumulations in Bouches-du-Rhône and Var do not require, at this time, a move to orange alert.
Rainfall intensities will begin to decrease Tuesday afternoon. Then, Tuesday evening, the disturbance will evacuate towards Italy. Improvement will therefore be rapid during the afternoon.
During this episode, accumulations could reach and exceed 150 mm in the Cévennes, which is usual during Cévennes episodes. But very significant accumulations are expected as far as Burgundy and Auvergne, passing through the Rhône valley, where more unusual accumulations (50 to 100 mm) could be observed. The situation could become delicate in these areas, even in the plains.
These heavy rains will therefore water large regions, some of which have already experienced heavy rains in September. The soils are already saturated and the risk of hydrological reaction will be significant.
On this episode, we expect:
This precipitation promises to be very intense between Languedoc and the Cévennes, over a “relatively short” duration not exceeding 24 hours.
The accumulations could, in 24 hours, reach 50 to 100 mm on average from the Massif Central to Franche-Comté via Lyon as well as the Var and the Alpes-Maritimes, corresponding to 2 weeks to 1 month of rain. In the Ardèche Cévennes, accumulations could rise to 200 mm. Risks of overflowing or flooding of rivers as well as occasional flooding are possible, especially as this precipitation will fall on soils already saturated with humidity, mainly from Burgundy to Auvergne.
In the PACA region, the accumulations will be between 40 and 60 mm, with possible peaks of 80 to 100 mm in the hinterland of the Alpes-Maritimes, which is notable.
