Weather warnings: heavy showers and thunderstorms along the English Channel

Weather warnings: heavy showers and thunderstorms along the English Channel

Weather warnings: heavy showers and thunderstorms along the English Channel

Of Regis CREPET, meteorologist

Warning for heavy rain from the North Channel

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From Thursday 8 September at 2.00 pm to Friday 9 September at 6.00 pm

Situation

A depression is circulating very slowly over England. It is the cold drop that has been spinning around Ireland since this weekend and is advancing very slowly towards the North Sea, which it will reach on Friday evening. It is responsible for the unstable and cooler climate over a broad northern half of France, with a succession of significant rainfall along the Channel coasts, mainly from Normandy to Upper France.

Heavy stormy downpours continue throughout the day, locally causing accumulations of up to 20-30mm throughout the day, sometimes falling over short periods. Accumulations that could approach 50 mm are expected in Picardy and in the Côte d’Opale.
This situation can lead to runoff and some flooding at low points and on secondary roads. It will be necessary to monitor, until Friday, the possible reaction of the Boulonnais rivers, which could suffer a rise in their level.
These sustained showers, sometimes stormy, will continue (during the night and Friday morning north of the Seine. Boulonnais is the sector most exposed to abundant accumulations of rain, which can occasionally reach 50-60 mm.

At the same time, strong gusts of wind can occur when the strongest thunderstorms pass, with tornado phenomena, such as tornadoes along the coast.

Observation

At 17, thunderstorms with lightning strikes Normandy, spreading towards Picardy. Some showers are sustained, with hourly accumulations reaching 7mm locally in Calvados. The strengthening of downpours and their generalization north of the Seine is expected after 6 pm, in the evening and throughout the night.

At 15, showers continue to multiply from the shores of the English Channel to the Paris Basin to the northern borders. Sometimes they are strong and stormy.

At 12, heavy downpours hit the Boulonnais and the Côte d’Opale, in Pas-de-Calais. In addition, showers tended to develop gradually throughout the Northwest, only to increase in intensity this afternoon.

At 10 o’clock, the showers were relatively light and few. However, a rainy front approached the Pas-de-Calais coast at the level of Boulonnais. However, the strongest intensity of these showers is expected in the afternoon.

This morning, the depression responsible for this disturbed weather, clearly visible on satellite images, is found in the Irish Sea at 1000 hPa and begins its slow progression towards England.
After the strong and frequent stormy downpours of the night between the Boulogne-sur-Mer and Calais regions, which generated accumulations of up to 49 mm in Boulogne, equivalent to 3 weeks of rainfall, new downpours are approaching the Atlantic coast. But during the morning a truce was established on the coasts of the Channel.

Evolution

Tonight and into the night, showers will be sustained north of the Seine. The strongest are concentrated on the Opal Coast, the North and the Pas-de-Calais. They continue overnight on these departments of Upper France, with accumulations that can reach a total of 50-80 mm on the hilly sectors of Boulonnais. Peaks of almost 100 mm are possible until Friday at noon at the end of the afternoon. Small streams flowing down the hills may react, but the very low levels following the summer drought will limit the risk of flooding. We can fear above all the outflow on the circulation axes.

This Friday, thein Côte d’opale, the North and Pas-de-Calais are mainly affected by these repeated strong thunderstorms, especially between 11am and 5pm. At the end of the afternoon and in the evening the most sustained showers and thunderstorms will break out in the interior: from the Aisne to the Ardennes with the risk of strong gusts of wind and small hail showers. The new accumulations for this Friday could reach 15-40mm, which could bring the total of the episode between 80 and 100mm in the hills of Boulogne-sur-mer.
Note the persistence of a moderate to fairly strong westerly wind, between 60 and 70 km / h, locally 80 km / h towards Cap Blanc Nez. The sea is strong, which requires caution if you are on the beach.

List of departments concerned

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