AIR Worldwide reports that extra-tropical cyclone Niklas, currently battering northern Europe with gale-force winds, “is reportedly one of the worst storms to affect Germany in recent years. High winds and heavy rains from Niklas have caused serious building damage in Germany, and triggered flood warnings across central and southern Germany.

Before hitting Germany Niklas struck the UK on Monday night with “wind gusts of nearly 128 km/h [79.5 mph] on the Norfolk coast,” as the storm moved eastward from the North Sea into the Baltic. Niklas was anticipated to continue its slow northeastward motion.

“The 2015 season has been characterized as a North Atlantic Oscillation (NAO) positive phase, with a higher-than-normal subtropical high (Azores high) and a lower-than-normal Icelandic low reaching from Greenland to the Baltic states,” said Sebastian Diebel from AIR Worldwide. “The increased pressure differential causes westerly winds to intensify between 50-60°N latitude, which favors stronger winter storms crossing the Atlantic Ocean.

“On March 28, a weak low pressure system (Mike) formed west of Iceland, and then rapidly developed and moved into the UK on March 29,” he continued. Diebel described Niklas, which formed on March 29, as even “more intense than Mike. In the meantime, Mike continued to strengthen and migrated into the Baltic Sea, leading to steady rain and strong winds over western and central Europe, particularly Germany.”

Mike’s highest wind speeds of 151 km/h [app. 94 mph] “were detected at the meteorological weather station on the Brocken, the highest peak in the Harz mountain range, located in Saxony-Anhalt,” AIR said. “On March 30, Niklas strengthened and began to follow a path similar to the one taken by Mike the previous day. However, Mike began to weaken as it moved into Sweden and Finland on March 30.”

Diebel explained that by March 31 Niklas had “developed into a strong storm centered over Denmark and the southern Baltic Sea, bringing high winds and heavy precipitation to Germany and parts of Great Britain.

“With wind gusts of more than 190 km/h [118 mph] (recorded on Zugspitze, Germany’s highest mountain), Niklas gave Germany a heavy battering on Tuesday. In fact, the German Weather Service issued a severe weather warning for northern and southeast Germany, with wind gusts from 10 to 11 on the Beaufort scale anticipated, and winds of up to 12 on the Beaufort scale projected on mountaintops.”

AIR Worldwide’s Dr. Bernhard Reinhardt said: “By the evening of March 31, the cold front of Niklas arrived in the alpine region of Germany, causing widespread intense precipitation and strong squalls. By blocking and reflecting Niklas’ strong winds, the mountains are causing additional intensification of the wind speeds and precipitation in the alpine forestland. Wind measurements for Niklas across Germany range from 137 km/h [118 mph] in Stötten auf der Ostalb, 151 km/h [93.827 mph] in Feldberg im Schwarzwald, 150 km/h [93.206 mph] in Großen Arber, up to the maximum reported measurement of 192 km/h [119.3 mph] on Germany’s highest mountain, Zugspitze.”

Dr. Reinhardt noted: “Currently, Niklas is anticipated to continue to move north and east, and weaken into Wednesday. By Saturday, normal weather conditions in the region are anticipated.”

On March 29 and 30, high winds from ETC Mike felled trees in parts of Germany, leading to delays in train service and highway closures. “This storm, however, caused much less damage than ETC Niklas, which struck the same region shortly thereafter,” according to AIR’s report. Damages in the UK included felled trees that disrupted both road and railway travel. Roadways on bridges were closed as a precaution.

The report said “winds in Munich are reportedly strong enough to knock pedestrians off their feet. Indeed, in parts of Germany, wind gusts from Niklas have overturned trucks.” There is also some “severe building damage due to high winds” in parts of Germany, as well as fallen trees that have “caused damage to roofs and cars.”

According to Germany’s national weather center, Deutsche Wetter Dienst (DWD), “heavy rain from Niklas is causing flooding in central and southern Germany. In some locations, the downpour has washed away soil, undermining trees and buildings and causing them to topple or collapse.”

Niklas has also caused “major delays to the country’s domestic and international train service. According to Deutsche Bahn, the storm has caused major delays and cancellations to long distance trains in Lower Saxony, Mecklenburg-Western Pomerania, North Rheine-Westphalia, Bavaria, and Baden-Würrtemberg. In addition, at least two trains collided with, or were hit by, fallen trees. High winds and heavy rains from ETC Niklas resulted in flight cancelations at airports in Schiphol, Frankfurt, Hamburg, Berlin, and Munich.”

The storm has also “caused widespread damage to building façades and roofs across Germany, Austria, and Switzerland, including fallen roof tiles. In some cases, light wooden or metal roofs were completely torn off; for example, in Zurich, Switzerland, a metal roof was ripped off a church. Also in Switzerland, the roof of a chocolate factory in Flawil, St. Gallen, was damaged, causing business interruption as well as property damage. In Luzern, Switzerland, the façade of a mid-rise residential building was damaged.

“Damage from Niklas has also been reported in the Netherlands, Belgium, and the Czech Republic. For example, in Belgium, many trees were uprooted by the storm and hundreds of homes experienced power outages.”

According to AIR, “most of the residential buildings in the United Kingdom are detached, semi-detached, or terraced (row) houses and are primarily of masonry construction. Single family homes in Germany, Denmark, the Netherlands, and Poland, are also predominantly of masonry construction, although a small percentage are wood frame, and are mostly low-rise. Sweden and Finland’s building stock have a much higher percentage of wood frame buildings.

“Mid-rise residential buildings generally have exterior non-load bearing walls made of masonry, although they may have light-gauge steel stud walls or concrete panels. Under high winds, most of the damage in built up areas is to rooftops and chimneys of residences, although walls and windows are often damaged by flying debris. Large apartment and condominium buildings often have a higher level of engineering and are more resistant to wind damage. Also, wind damage ratios for tall buildings are lower because tall buildings are generally well designed and constructed. However, balconies, awnings, and sliding glass doors are susceptible to wind damage.”

AIR also indicated that “commercial exposures use a wider variety of construction types. Smaller buildings are usually masonry and perform similarly to residential buildings under strong winds. Larger buildings are generally reinforced concrete or steel, and wind damage is typically to nonstructural components such as mechanical equipment, roofing, cladding, and windows. Large commercial buildings often have a large amount of external glass, which is quite vulnerable to wind damage.”

AIR, however, also noted that “floods can affect a significant portion of low and mid-rise buildings, particularly the cellars. Risk is particularly high for finished cellars with furniture and appliances; some may contain entire apartments. Usually, heavily used cellars have better flood defense mechanisms than unfinished ones. For tall buildings, flood vulnerability is usually mitigated by flood defenses, although lower floors and cellars often contain services, fixtures, and electrical and mechanical fittings.

Dr. Reinhardt concluded: “As of March 31, 2015, ETC Mike and ETC Niklas are located over the Baltic Sea. Centered just offshore of the southern tip of Sweden, high winds from ETC Niklas are continuing to impact exposures in Germany. “

Source: AIR Worldwide