Extensive damage in the Southwest after the storms: why were they so violent?

Météo-France had warned. The Southwest was swept by thunderstorms on Monday afternoon. Eleven departments were placed on orange alert. Four were also affected by an orange alert for rain and flooding. Hailstorms and torrential rains hit the Southwest late Monday, affecting the towns of Montech (Tarn-et-Garonne) and Eugénie-les-Bains (Landes), which were hit by flooding.

Just like in Tonneins in Lot-et-Garonne, where a TGV train connecting Paris to Toulouse had to make an emergency stop, part of the tracks having been washed away by the water. Passengers were evacuated in the evening.

Géraldine de Mori, head of the RMC weather and environment service, explains this phenomenon: "We had a cold drop at altitude that positioned itself above the warm, humid air of the Mediterranean. This is what fueled supercell thunderstorms that remained stationary."

"This stationary side produced torrential rain with several records: 111 mm of rain in Puycelsi (Tarn), 80 mm in Saint-Félix-Lauragais (Haute-Garonne) and 63 mm in Condom (Gers)," she explains.

But why are they so powerful? Alix Roumagnac, president of the weather analysis service Predict, adds: "They have a lot of energy and are very large in size. They will bring larger hailstones and longer durations, and therefore very serious consequences."

In comparison, "these are the typical storms that produce tornadoes in the United States ." According to him, "recently we have seen them from time to time in France when we have a very particular context with very, very high temperatures on the ground when a depression arrives with cold air at altitude."

But that's not all. There was also significant electrical activity. More than 22,600 lightning strikes were detected in France on Monday, mainly in the southwest. The most powerful lightning strike of the day occurred in Lavaurette (Tarn-et-Garonne), at 516 kiloamperes, according to Keraunos , a French firm specializing in severe storm meteorology.

"It's 20 times more violent than the average lightning strike during the day," the specialist explained on RMC .

However, even though the episode was only temporary, it caused a lot of damage in the Southwest.

In Lot-et-Garonne, the bad weather mainly affected the Tonneins area, where a collapse of ballast beneath a railway line caused the interruption of rail traffic on the Bordeaux-Toulouse line. A TGV train was forced to stop on the track, with its 507 passengers evacuated by bus to a municipal hall in Tonneins.

The bad weather also caused a tree to fall in the center of Toulouse in Haute-Garonne, flooding of secondary roads and evacuations of schools. Firefighters carried out hundreds of interventions in the departments placed on orange alert by Météo-France .

A little further south, in Toulouse, two middle schools will be unable to open their doors this Tuesday morning. Specifically, in Aurignac and Pins-Justaret. No casualties have been reported, but the storms caused significant material damage. Residents are in shock.

In just a few minutes, a white carpet covered Dominique's garden: "There were at least 10 cm of hailstones. It was like being at a winter sports resort, in the middle of winter, you couldn't even see the asphalt anymore." She was in her car when the hail started to fall. So she hurried home to safety.

"It was absolutely enormous and then a hell of a noise, a machine-gun blast," she describes.

In her town of Fousseret, a school building was damaged. 63 students had to be taken to a nearby daycare center for shelter. Many roofs were damaged by hailstones. Some were the size of tennis balls, 7 centimeters in diameter. It left a mark on Lilou's car: "It's dented everywhere. It broke the rearview mirror, the windshield. I went home, I was really scared too."

"We've had hailstones before, but they lasted a minute. This time, it lasted a good twenty minutes, maybe even 25 or 30 minutes," the young woman told RMC.

The storms have now shifted eastward. They could be just as intense in the PACA region, with a risk of waterspouts or tornadoes, particularly in the Var region. The only department still placed on orange alert for thunderstorms and rain and flooding this Tuesday morning, at least until noon. Météo-France also warns that rainfall could reach 80 to 120 mm in three hours.