Thunderstorm outbreak slams Europe, with damaging tornado in France

A late-season severe weather outbreak rocked Western Europe on Sunday, bringing damaging winds, large hail and at least one destructive tornado. The storms came at the conclusion of an unusually warm spell, with temperatures that ranged 10 to 15 degrees above average for mid- to late October.

The most severe tornado appears to have struck Bihucourt, in the Pas-de-Calais region of northern France, about 90 miles north of Paris. Videos and photos reveal snapped utility poles, destroyed buildings, flipped vehicles and industrial structures left as piles of splintered wood.

The storm “ravaged the near-totality of the village. … Some homes were razed, collapsed, their were roofs ripped off. The church is partially destroyed,” Bihucourt Mayor Benoit-Vincent Caille said on public broadcaster France-Info, the Associated Press reported.

It’s estimated that about 300 tornadoes hit Europe every year, with between one- and two-dozen annually in France. They’re more common in the summer months, but autumn storm systems stemming from the clash of the seasons can spin up severe storms, too.

There were no reports of fatalities from the storms, which also impacted the United Kingdom, Belgium and the Netherlands, though Reuters confirmed one minor injury in the French town where the tornado hit.

Severe storms swept from France to the Netherlands

A broken line of thunderstorms formed over the northern end of the Bay of Biscay along France’s west coast during the afternoon hours, expanding into a broken line oriented northwest to southeast as it crossed over northwestern France. As the storms progressed northeast, they tapped into anomalously warm and humid air and intensified.

The Associated Press reported 60 homes were damaged in Conty and O-de-Selle, France, about 40 miles south of where the tornado occurred. It’s unclear if the damage was associated with an earlier tornado from the same thunderstorm or the result of straight-line winds. Intermittent minor wind damage occurred in Belgium and the Netherlands, too.

The storms also blitzed southeast England.

Strong winds blew through Embankment Station on the London Underground. Social media video showed a maelstrom of shredded leaves sailing through the air like aggressive confetti.

In France, more than 50,000 lightning strikes were tallied as the storms passed. The U.K. Met office reported 40,000 lightning strikes in Britain.

The setup

Temperatures over the past five days have run about 10 degrees above seasonal norms for this time in France and across the U.K. That allowed for the buildup of sufficient CAPE, or Convective Available Potential Energy – or fuel – for strong storms. What was needed was a trigger.

Meanwhile, a dip in the jet stream filled with high altitude cold air, low pressure and spin, was parked over the northeast Atlantic at the same longitude as Iceland. Around that broader trough, smaller shortwaves, or more localized disturbances, have been rotating.

One of them passed over northwestern France on Sunday afternoon. Frigid air aloft chilled the upper atmosphere, allowing surface air to more efficiently rise and form storms, while the influx of vorticity, or spin, enhanced upward motion further.

Meanwhile, a simulated weather balloon sounding, or vertical profile of the atmosphere, indicated the presence of wind shear, or a change of wind speed and/or direction with height.

Storms that develop in sheared environments have a proclivity to rotate, since they’re subjected to varying forces at different altitudes.

A French storm chaser captured a photo depicting a rotating thunderstorm, known as a supercell, which appears to have produced a tornado. On the right beneath the storm, dark curtains of rain and hail can be seen cascading to the ground in the downdraft region of the storm. Toward the left, or south, a brighter rain-free region can be seen. That’s the updraft region, characterized by upward-moving air spiraling into the storm.

Less turbulent weather is forecast for Western Europe for the next few days, although a storm front late in the week and into the weekend could bring some gusty downpours from Portugal into the United Kingdom.