new weather vigilance in France 05/09/2022

Storm during the night of September 4 to 5, 2022 in Vendée – Via Twitter @Troospea

A situation favorable to thunderstorms:

The situation is unstable this week in France with the gradual approach of a low-pressure area via the Atlantic and the British Isles.

Animation of geopotentials over Western Europe from Monday 5 to Friday 9 September 2022 – GFS model via WX CHARTS

This low pressure area induces an unstable South/South-West flow over a large part of France from the beginning of the week with the formation of successive stormy waves in many regions until the end of the week.

Animation of precipitation over France from Monday 5 to Friday 9 September 2022 – ICON model via WX CHARTS

If the storms concern the North and the North-West of the country between today and tomorrow with locally strong intensities at the end of the dayit is in particular in the East and South-East of the country that these are expected to be the most active and most frequent from tomorrow, Tuesday, in particular due to a more frank air mass conflict in these sectors. .

Further north and west, the arrival of oceanic air that is less warm on the ground and cooler at altitude should in fact cause less instability from the middle of the week and thus reduce the risk of severe thunderstorms.

Atmospheric situation of Wednesday September 7 over Western Europe – ECMWF, modified by Météo-Villes

Many risks of thunderstorms in the coming days in France

Already this Monday, occasionally active thunderstorms are formed between the afternoon and the evening of the Pyrenees in the North, producing in particular locally marked precipitation, sometimes hail mbut mostly strong gusts of wind (loc. >90-100km/h) under the strongest cells between the Centre, Île-de-France and Hauts-de-France. This stormy risk will evacuate towards Belgium and Germany during the next night.

Animation of precipitation until Tuesday, September 6 in the middle of the night – Aroma model via WX CHARTS

Due to the intensity of the storms expected for the end of the day and in particular the risk gusts of wind that can exceed 80-100km/hMétéo-France placed at the beginning of the afternoon of this Monday 12 departments ranging from Cher to Aisne via the whole of Île-de-France in orange vigilance until the end of the next evening.

At the same time, the departments of Gard and Hérault are also placed on orange alert from the end of the night from Monday to Tuesday to a risk of thunderstorms that are sometimes violent but above all locally stationary and excessively rainy.

Vigilance card for Monday September 5, 2022 at 4 p.m. – Meteo France

Tuesday September 6: locally marked thunderstorm risk from South to North

The situation is changing little on Tuesday with a flow from the South-West remaining unstable and dynamic over France. If the morning promises to be generally unstable, except near Brittany and Languedoc, the risk of thunderstorms will increase again from the afternoon with thunderstorms spreading to the regions located from the Pyrenees to the North, passing through the Massif-Central and the Centre.

Stormy risk envisaged for this Tuesday, September 6, 2022 – Weather-Cities

Several sectors will be to watch this Tuesday. From Cotentin to the North, storms could generate locally marked accumulations as they pass, which can exceed 30-40mm in a few hours and cause significant runoff, even local flooding.

From the Massif-Central to the North-East, the storms are also expected to be powerful between the afternoon and the evening with in particular a risk of strong gusts of wind which can exceed 80-100 km/h, locally of hail and intense precipitation which can also cause local flooding.

Animation of gusts of wind as thunderstorms pass during the day of Tuesday, September 6, 2022 – Aroma model via WX CHARTS

Near Languedoc, thunderstorms are expected to be less widespread but could be particularly rainy due in particular to a maritime flow bringing very high instability and a high precipitable water content of the air mass coming directly from the Mediterranean.

Significant precipitable water content and very strong instability near Languedoc during the day of September 6 – Aroma model via WX CHARTS

Given the circulation of small convergence zones between the Hérault, the Gard and the west of the Bouches-du-Rhône, stationary storm cells may form at the start of the day in isolation and last until the following night. These can sometimes give marked accumulations that can exceed 60-80mm in a few hours or even locally 100mm if a storm manages to stay longer in a particular sector.

The risk of thunderstorms will decline over most regions overnight from Tuesday to Wednesday, persisting longer near Languedoc.

Wednesday, September 7: risk of severe thunderstorm in the South-East

This Wednesday the depression is advancing more frankly towards France with the arrival of more oceanic air from the West and North-West of the country. The hot and unstable air will persist over the Southeast where the stormy activity is expected to be the most marked during the day, even if sometimes stormy showers could circulate in many other regions.

Stormy risk envisaged for this Wednesday, September 7, 2022 – Weather-Cities

It is indeed on the South-East of France that the instability promises to be the most important during this day of Wednesday with the formation of sometimes virulent thunderstorms from the Massif-Central to the Alps via the Rhone Valley, Languedoc and western Provence. In these sectors, thunderstorms will once again be likely to produce strong gusts of wind, hail and especially heavy rain can bring significant accumulations in a few hours and therefore a risk of local flooding.

The situation will also remain under surveillance near the Gulf of Lion where new stationary thunderstorms are likely to form, especially between the afternoon, the evening and the following night. The sector remains subject to very humid and unstable air favorable to the formation of very rainy storms. A situation that will induce particular vigilance, especially in areas already affected the day before.

Animation of precipitation totals over 24 hours during the day of September 7 and the following night – Arpeggio model via WX CHARTS

The risk of thunderstorms should also persist for a good part of the following night, especially between the Gulf of Lion, the Alps and the Rhône valley. with intensities remaining marked and a risk of significant accumulations of precipitation in these sectors.

Thursday September 8 and Friday September 9: a stormy risk retreating over the country

The cooler oceanic air at altitude and less unstable should advance more frankly over France from Thursday and thus generate less marked instability over the country. Nevertheless, heavy showers, sometimes stormy, will remain present in the North of the country over these two days due to the proximity to the low pressure trough circulating over the British Isles.

On the South-East, some residual stormy showers could also concern the interior of the Côte d’Azur on Thursday, however remaining of classic intensity.

Stormy risk envisaged for this Thursday 8 and this Friday 9 September 2022 – Weather-Cities

This stormy risk should not present any particular severity unlike the previous days, however, we will monitor the risk of temporary heavy rainfall over these two days under the numerous showers circulating in the North of the country and especially near the Channel coasts.

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