The weather will be agitated Sunday over a large part of the country with thunderstorms sometimes strong and large amounts of rain to fear over the Southwest and the Center, where an orange vigilance for rain-flood was issued for a total of ten departments , said Météo-France on Saturday.
An exceptional event expected
This alert, valid from Sunday 2 p.m., first concerned the Gironde, Landes, Gers, Pyrénées-Atlantiques and Hautes-Pyrénées. It was extended Sunday morning to Charente-Maritime and Lot-et-Garonne in the west as well as to Indre-et-Loire, Loir-et-Cher and Loiret in the Center. It is the duration of the sustained rains as well as their fairly wide geographical domain that make this event exceptional. The quantities forecast in 24/48 hours could thus be close to the centennial values, according to the forecaster.
After the thunderstorm wave of the night when the thunderstorms were punctually well active, a lull takes shape at the beginning of the morning, but a new rain-storm degradation is taking place by the southwest. The rains, often moderate, sometimes heavy, then overflow from the Pyrenees towards the plain, as far as the Garonne valley, and take on a stormy character. It is difficult to identify successive waves but between Sunday afternoon and Monday noon, the periods of heavy precipitation follow one another, giving significant, even sometimes exceptional, accumulations. Their repetition is the dominant stake, the stormy character being drowned in the mass.
Hail falls possible
Some gusts of wind around 60/70 km / h are possible as well as hailstorms under the most virulent thunderstorms. Rainfall intensities could frequently reach 20 to 30 mm (or liters / m²) per hour. We thus expect throughout the episode, 50 to 100 mm almost generalized on the departments placed in orange vigilance. From Basque Piedmont and Bigorre to Armagnac and the Bassin d'Arcachon, it is even possible to locally reach 100 to 150 mm (i.e. 1 to 2 months of precipitation) in less than 36 hours, which corresponds to return times sometimes around 100 years.