Weather Alert: Strong storms in the southeast and heavy rain in the north

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Situation

After a calm and anticyclonic week, weather conditions changed drastically. Conditions have turned to low pressure, establishing a highly disturbed northwesterly flow that collides with a rising warm air mass in the Mediterranean.

This development causes a thermal conflict, conducive until Saturday night to heavy stormy rains in the Mediterranean regions. This episode generates heavy rains, but is still too short to qualify as a Mediterranean episode. As a reminder, a Mediterranean episode is classified by accumulated rainfall greater than 200 mm, in 24 hours, in one or more departments of the southeast. This is not the case this Saturday, because the most important accumulations will reach 80 to 120 mm at most as the strongest storms pass.

In the middle of this system of low pressures, a minium dug in front of the Norman coast causing a very strong instability in the neighboring regions of the Channel this Saturday.

In addition, in a very unstable flow from the northwest, strong showers also occur in the Pyrenees-Atlantiques, and in particular in the Basque Country.

Observation

This Saturday

At 9 in the morning, the stormy rains concern Provence Côte d’Azur, where punctually they are quite intense. Heavy downpours also occur in Hauts-de-France: in Calais (62), 80 mm of rain have fallen since last night, that is, as much as falls on average in September. This is an absolute record for daily rainfall for all months in this city.

At 7 a.m., having swept Languedoc-Roussillon tonight, heavy stormy rains are currently reaching the east of the Rhône, that is, the Provence Alpes Côte d’Azur. Last night in Languedoc up to 94 mm of rain fell in Cardet (30) between 1 and 5 in the morning, which corresponds to a month of rainfall. The wind reached 117 km/h in Grau-du-Roi (30) when a violent storm passed over the Gard coast.

In the north, continuous heavy rains continue from Nord-pas-de-Calais to Calvados since last night. 77mm of rain has already fallen in Calais (62), corresponding to three weeks of precipitation.

Evolution

Here is the timeline of this degradation.

For the southeast:

This morning, low pressure moves away from the coast of Provence. In its wake, it causes a brief episode of heavy thunderstorm rain lasting 2 to 3 hours in the Var and the Alpes de Haute Provence, with accumulations of up to 30 to 60 mm in 1 to 2 hours very locally.

at the end of the morningthe storms will sweep the Maritime Alps, being able to throw strong sheets of water (up to 50 mm in 1 to 2 hours locally).

This afternoon, It is Corsica’s turn to suffer an episode of heavy rains and thunderstorms that will cross the island from west to east, which can bring 30 to 60 mm of water to the western relief of the island.

Tonight, storms will evacuate towards Italy, ending this brief but sometimes powerful bout of bad weather.

For the North:

In the midst of the vast low pressure system, another low pressure has developed in the English Channel. It remains until Saturday night, moving very slowly towards the Pays de la Loire. At the return of the occlusion around this little mobile depression, there are heavy stormy downpours from Normandy to Nord-Pas-de-Calais, which can bring 40 to 80 mm of water, which could cause very localized flooding. , in Seine-Maritime in particular.

These are the main characteristics of this degradation.

– intense and sometimes stormy rains, in 2h to 4h in PACA, Corsica, with layers of water that can locally exceed 80 mm in Corsica
– under the strongest storms, risks of flooding, but these should remain relatively limited due to dry soils
– in Normandy, the local accumulated precipitation may reach 80 mm this Saturday and approach the daily rainfall records for the month of September

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