Of
Monday April 8 at 12:00 At
Tuesday April 9 at 9:00 a.m.
Situation
A depression is forming off the coast of Portugal this Sunday evening. Named Pierrick, this storm, carried by a very dynamic southwest jet stream at 200 km/h, rises very quickly towards Brittany on Monday evening, deepening at 985 hPa. It reaches the North Sea on Tuesday morning via the Channel basin.
This depression causes a violent gale from Brittany to the Channel coasts with gusts which can reach 90 to 110 km/h, occasionally speeds 10 to 20% higher under storm squalls and on exposed capes and coasts.
Due to the high tidal coefficients (110 Monday and 113 Tuesday), the risk of coastal submersion is high during this period at high tide, especially as waves of 4 to 6 meters will propagate from the sea towards the side.
Associated with this depression, a disturbance crosses France from west to east. This disturbance collides with very warm air which rises from the Maghreb to Germany. As a result, thunderstorms form on Monday evening from the Pyrenees towards central France. These storms, occasionally strong, can be accompanied by hail and sudden, brutal winds.
During the night from Monday to Tuesday, this disturbance quickly reached the east of the country where the situation is under surveillance with a risk of heavy stormy rain, requiring a possible extension of our alert to other departments and regions.
Observation
Sunday
At 18 h, the Pierrick depression, responsible for the bad weather to come, began to form off the coast of La Coruña and began its rise towards the Bay of Biscay.
Evolution
Regarding the gale
Monday afternoon, as storm Pierrick approaches, the weather becomes heavy over France with the development of large, threatening cumulus clouds from the Pyrenees to central France. From Normandy to Nord-Pas-de-Calais, brief but strong storms develop. In Brittany, the south wind is strengthening.
Monday evening the real degradation begins. The south wind is rapidly gaining strength, reaching 90 to 110 km/h in Brittany, up to 120 to 130 km/h on the coasts of the Finistère department placed on orange alert by our services. At the same time, the disturbance is taking place between the Pyrenees and the central regions with storms that are sometimes strong and occasionally accompanied by hail.
During the night from Monday to Tuesday, the depression sweeps the entire Channel basin with gusts reaching 100 km/h. Initially oriented to the south, the wind turns to the west then to the northwest. Convective gusts of 100 km/h are widespread across the entire Channel basin, up to the Opal Coast at the end of the night.
Monday morning, while the wind weakens on the Breton coasts, it remains violent from Normandy to Nord-Pas-de-Calais with gusts in squalls at 100 km/h along the seaside, up to 130 km/h on the capes and exposed ribs. With the shift of the wind to the west and northwest, a coefficient of 110 and waves of 3 to 6 meters coming from the sea, the risk of submersion will become significant at the time of high seas especially as the storm surge reaches 50 to 70 cm.
Monday afternoon, the wind will begin to weaken. But, due to the strong instability, powerful convective gusts persist for a few hours from Seine-Maritime to Nord-Pas-de-Calais.
Regarding storms
Monday afternoon, occasionally strong storms break out from Normandy to Hauts-de-France. These storms are brief, but very electric.
It’s Monday evening that the situation is the most delicate. Indeed, occasionally strong storms develop from the Pyrenees in the center of the country to the Ardennes as the cold front passes. These storms are organized online. They can be accompanied by hail and powerful gusts of 90 km/h, with the risk of agricultural damage.
During the night from Monday to Tuesday, storms reach the regions east of the Rhône and the Saône during the night from Monday to Tuesday. These are heavy stormy rains which are not of a truly aggravating nature for the moment.
Tuesday morning, the heavy stormy rains are concentrated from Franche-Comté to Rhône-Alpes to the Cévennes (reason for which this special press release could be extended). Total rainfall (up to 30 to 50 mm) is expected to be quite significant. Due to saturated soils, these new rains present risks of hydrological reactions (floods, floods). The situation is also under surveillance for Provence Alpes Côte d’Azur where a fairly significant stormy spell is likely to occur on Tuesday. In the mountains, heavy snowfall is expected from 1,300 meters above sea level in the Alps, which could increase the risk of avalanches.
Tuesday afternoon, the disturbance will evacuate towards Italy and Switzerland and the precipitation will weaken. But, with the plunge of cold air into the Mediterranean, the mistral and tramontane will take over from the rains and storms. They will blow violently from Tuesday evening to Wednesday morning, with gusts reaching more than 100 km/h from the lower Rhône valley to the Camargue to the Provencal coast as well as in the Roussillon plain to the Narbonne region.
