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Rare 1,000-mile derecho event crosses Europe, killing at least a dozen

Gusts traveled from Corsica to southern Czech Republic, hitting speeds of up to 140 mph at times

A photograph taken from the French Riviera city of Nice shows lightning flashes in a supercell thunderstorm over the Mediterranean sea this week. (Valery Hache/AFP/Getty Images)
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A massive storm complex traveled a nearly 1,000-mile path across Europe with winds up to 140 mph, causing devastation on the French island of Corsica and to landmarks in Venice, before moving on to inflict major wind damage in parts of Austria and Slovakia. Reports state that at least a dozen people have been killed in the storm, which also knocked out power for thousands.

Experts said that the storm complex appeared to meet the pattern of a derecho, an exceptionally widespread and long-lived windstorm that is uncommon in this region. Coherent gusts traveled more than 600 miles from Corsica to the southern Czech Republic, hitting speeds up to 140 mph at times. The storms originated near the island of Mallorca before sweeping across the Mediterranean and into Europe, with a total track length of about 1,000 miles.

“I think it’s quite likely that the Mediterranean event indeed was a derecho,” said Johannes Dahl, co-founder of the European Storm Forecast Experiment (ESTOFEX). “I don’t think it’s common to have derecho-type events in this area (even less common than derechos in the rest of Europe).”

Derechos in Europe are rare, only occurring about once a year. Such convective wind storms that do occur are typically smaller and less intense than Thursday’s.

Path of destruction

The storm complex was moving exceptionally fast Thursday morning, adding to its wind damage. The intense line of storms hit the Corsican capital of Ajaccio on the southwest coast at 8:15 a.m. local time. An hour later, it reached the northeast tip — roughly a forward speed of 70 mph.

Dramatic video from Corsica’s Ajaccio Napoleon Bonaparte Airport shows the extreme destruction that 136 mph gusts, equivalent to the force of a Category 4 hurricane, can cause. The winds damaged an Airbus A319, a commercial jet that can hold up to 156 passengers, with one of its wingtips bent by the storm, according to reporting from Airlive.

Preliminary reports of gusts in Corsica include: 140 mph (225 km/h) in Marignana, 128 mph (206 km/h) in L'Île Rousse, 122 mph (197 km/h) at Calvi, and 116 mph (188 km/h) in Bocognano, among others.

At least five people were killed in and around the French island during the storm, according to the Associated Press. Several others were injured, and at least a dozen people were hospitalized in Corsica.

The storm caused dramatic damage across northern Italy. In Venice, the rowdy winds tossed tables and chairs like toys in the popular St. Mark’s Square, and pieces of brick were ripped straight off St. Mark’s bell tower, the tallest structure in the city.

In Piombino, a dramatic video of the storm shows a Ferris wheel spinning rapidly, its carriages jostling out of control as the howling winds affected the structure. According to the Associated Press, hailstones the size of walnuts caused substantial damage in the Liguria region of Italy, breaking windows and damaging farmlands that had already been scorched by drought. Reports indicated that at least two people in Italy were killed in the storm.

The storm continued to bring intense lightning and strong winds even after ripping through parts of Northern Italy. A video from Kranj, Slovenia, shows intense winds ripping off the roof of what appears to be a large apartment complex, damaging cars parked below.

In Austria, another astonishing video shows high-voltage power masts bent in half. According to reporting from Austrian broadcaster ORF, at least 65,000 people in Styria, a province in the heart of Austria, lost power during the storm, which brought gusts of at least 86 mph (139 km/h).

The Austrian Red Cross confirmed that two children in Carinthia died in the storm, two were seriously injured, and 11 others were slightly to moderately injured.

Makings of a rare derecho

The storm’s peak winds were on par with some of the highest ever recorded outside the mountains in Europe. Such strong gusts in widespread fashion are uncommon in the region. A majority of widespread wind damage events occur in the fall through spring, typically coming from strong mid-latitude storm systems dancing along the jet stream.

About one derecho usually forms over Europe annually, although some years can feature several. Most of these convective wind storms are smaller and less intense than the swath that occurred Thursday, according to research by European Severe Storms Laboratory (ESSL) scientists.

To be a derecho, the wind storm must be at least 60 miles wide and leave 400 miles of damage. Even then, a complex of storms must have gusts of at least 58 mph across most of its length, with several gusts of at least 75 mph, according to the U.S. National Weather Service.

The storm handily passes those requirements, although it is rare for the region.

The storm “developed in the area (Corsica/ N Italy) where it is generally uncommon to see a derecho (but they do occur),” Mateusz Taszarek, researcher at Adam Mickiewicz University in Poland and ESTOFEX contributor, said in an email.

Stavros Dafis, a research associate at the National Observatory, said the extreme storm was probably enhanced by unusually warm waters. Sea surface temperatures were about 5 to 10 degrees (3 to 5 Celsius) above normal, helping increase storm intensity.

“The marine heat waves of the past few weeks have made the environment conducive for extreme thunderstorms,” wrote Dafis, who is also a forecaster at ESTOFEX.

Water temperatures often play a role in how much moisture is available in the atmosphere. Moisture acts as a fuel when combined with warmth. Unusually warm water around Corsica ensured that storms had plenty of juice.

“Typically the Mediterranean convective systems result in heavy rain and much less frequently in extremely severe wind gusts,” Tomas Pucik, a researcher with the European Severe Storms Laboratory, said in an email. “Having a windstorm instead is more rare and local forecasters have less experience with these types of events.”

Although the location and intensity are both unusual, this event is reminiscent of a derecho that struck Germany, including Berlin, in July 2002. That storm complex was responsible for eight deaths and 50 injuries.