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A highly unusual summer storm is bringing hurricane-force winds to western Europe, lashing the Netherlands and Germany and killing at least two people, according to the Associated Press. More akin to a powerful winter storm, the system even creates a destructive “sting jet” that mixes jetstream winds onto the ground, causing widespread damage and disruption.
Portal reported that the storm knocked down dozens of trees in Amsterdam on Wednesday, damaged cars and houseboats and injured several people. The news agency added that it was the worst storm on record to hit the Netherlands in the summer months and “the strongest overall since 2018,” according to weather agency Weeronline.
The German Weather Service, which gave Poly its name, warned of “extreme weather” in red, the highest level on its scale. They forecast “hurricane gusts” with wind gusts between 65 and 80 mph from the south, then switching to the west as Poly’s core pivoted through.
“Area-heavy damage to buildings is possible,” it said. “Trees can be uprooted and roof tiles, branches or objects can fall. Close all windows and doors! Secure outdoor items! In particular, keep your distance from buildings, trees, scaffolding and high-voltage power lines. Avoid staying outside if possible!”
Conditions are improving in the Netherlands after wind gusts of up to 92mph hit west of Amsterdam. As of Wednesday evening local time, wind speeds have calmed down again in the 40 to 55 mph range. Previous code orange alerts – the highest level issued – have been downgraded to code yellow alerts by the Royal Netherlands Meteorological Institute.
In Ijmuiden (Netherlands) gusts blew at a speed of 92 miles per hour. Gusts blew at 80.4mph in nearby Ijmond and 73.6mph in Amsterdam.
The Associated Press reported that the storm canceled or delayed hundreds of flights at Amsterdam’s Schiphol Airport, one of Europe’s busiest airports, while halting trains in the north of the Netherlands.
Poly is a strong low pressure system that developed Tuesday from a wide trough or southward meandering of the jet stream. A pocket of freezing air at high altitude, low pressure and vortices moved overhead, reinforcing a young surface deep over the English Channel. It has shifted north-northeast towards Belgium, Germany and the Netherlands and will shift towards Denmark and Sweden on Wednesday night, some of which will be weakened.
East of Poly across Russia lies an extensive high pressure system. The juxtaposition of the opposing systems created a sharp pressure gradient, or abrupt change in air pressure over a short distance, that was responsible for the strong winds that accompanied Poly’s arrival.
The presence of broadleaf trees has likely contributed significantly to the damage observed at poly to date.
A possible “Sting Jet”
Here is the radar of a rapid deepening #Storm #poly Moving ashore to the #Netherlands. This storm features a spike jet around the center of the circulation causing wind gusts in the 120-140 km/h range. Some heavy rainfall is also associated with the storm. pic.twitter.com/PFt0ublQHs
— East Scotland Wx (@EastScotland_Wx) July 5, 2023
At first glance, it appears that Poly wasn’t strong enough to create the winds it created, simply because the air flowed from high pressure to low pressure. It’s likely another mechanism was at play – a spike ray.
Sting Jets are narrow corridors of intense wind that form on the “enveloping” portion of a comma-shaped low-pressure system that is rapidly intensifying.
In the case of a rapidly strengthening nontropical system, the jet stream can drive moisture-laden air into an intrusion of dry air into the low-pressure system. As a result, the ice crystals, water droplets and precipitation within this shell evaporate quickly, causing the surrounding air to cool down. Because the cooled air is now suddenly denser than the surrounding air, it rapidly descends, hitting the ground and bringing jet stream winds with it. String jets can create channels with gusts of 80 to 100 mph – and occasionally higher.
They are an integral part of some of the worst storms to ever hit Western Europe. Their existence was postulated after the Great Storm of 1987 which killed 22 people in populous south-east England and adjacent western Europe. A 135 mph gust was measured at Pointe du Roc, Granville, Normandy, France. The wind downed an estimated 15 million trees and caused nearly $6 billion in damage.
Later re-analysis of data leading up to the unforeseen storm revealed the existence of “Sting Jets,” which have been observed dozens of times since.
Jason Samenow contributed to this report.
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