WEDNESDAY, OCTOBER 18, 2017
Extratropical Cyclone Andrea
1/6/2012 5:00:00 PM
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Final Posting 1/6/2012 5:00:00 PM  
Summary
Posting Date: 1/6/2012 5:00:00 PM
Current Situation

Windstorm Andrea passed through the U.K. earlier this week, fast on the heels of Windstorm Ulli, which brought widespread travel and power disruptions to Scotland. Andrea— the first named European storm of 2012— formed southwest of Iceland on Tuesday, 3 January.

Late Wednesday (4 January), Andrea passed to the north of the U.K., bringing strong winds, particularly to central England, and causing power outages and travel disruption. The system intensified as it traveled east. Early yesterday, Andrea was centered over Denmark with a central pressure of 964mb—down from 971mb the day before. In Germany today, the storm’s high winds have caused numerous roadway accidents, as well as power outages, ski resort closures, and flooding. Indeed, Germany has been hardest hit by this early January storm, with flooding impacting the country’s northern region and high winds extending as far south as Bavaria. Western Austria, where Andrea’s heavy winds toppled trees that blocked roads and disrupted power, was also impacted.

Meteorological Conditions

When Andrea formed southwest of Iceland, it had hurricane-force winds. Forecasts at that time warned of a very strong wind event for the UK, the Netherlands, Denmark and Germany; appropriate warnings were issued by each of the national weather services. The Met office issued yellow warnings for rainfall levels.

Andrea’s path brought it north of Scotland and through the North Sea, then south to Denmark and Poland. Its strongest winds—to the south of the storm’s track—were ultimately weaker than expected. Thus, Andrea caused less disruption in the United Kingdom than had Ulli earlier in the week. Due to Andrea’s southeastward path, however, it went into Germany, which Ulli had bypassed; thus, Andrea had higher wind speeds in Germany than its predecessor.

Typically, strong extratropical cyclones approaching Germany from the North Sea, as Andrea did, push water against the German coast, causing flooding. Indeed, there was flooding in the low-lying areas of Germany today (i.e., Hamburg). Also, because they obtain their energy from temperature gradients rather than from warm ocean water, which is the fuel for hurricanes, these storms can extend far inland. This explains why Andrea brought very strong wind gusts as far south as Bavaria today.

Figure 1: Andrea’s track and maximum observed wind speeds (3-second gusts) (Source: METAR).

Over the past few months, northern Europe has seen a number of significant storms pass through, beginning with Xaver and Yoda which impacted the region in late November. These were followed by Friedhelm in early December, both Joachim and Patrick (Dagmar) in late December, and Ulli (which formed on December 31st) in early January. This clustering effect of windstorms in Europe—storms following closely on the heels of one another—is a well-studied phenomenon and is explicitly accounted for in the AIR Extratropical Cyclone Model for Europe.

Building Stock

Residential building stock in the areas affected by Andrea is predominantly of masonry construction. For commercial exposures, however, and particularly for commercial exposures in Germany, the building stock uses a wider variety of construction materials. Smaller office buildings, hotels, and other smaller commercial structures are usually masonry but larger buildings are generally made of reinforced concrete or steel.

Little structural damage to these construction types is expected for wind speeds of the order widely experienced from Andrea, although damage to cladding, signage, and some isolated roof covering damage could occur. The flooding that occurred in Germany, however, may cause some damage; when residential buildings are subjected to floodwaters, most of the damage is limited to the basements, although the first floors of homes can also be submerged during severe flood events. In Germany, however, about 80% of all residential structures have basements, which alleviate the flood risk to floors above ground.

Reported Impacts

During Andrea’s passage over the United Kingdom, strong winds disrupted power to nearly 1,000 homes in Nottingham, 70 miles from the North Sea coast. Though Andrea impacted a region of the U.K. similar to that impacted by Ulli, its peak gusts were weaker, according to early meteorological observations from METAR stations in the UK. In Leeds and Bradford, England, peak gust recordings for Andrea were 120 km/h (about 75 mph). For Ulli, by contrast, the highest gust speeds were 170 km/h (106 mph), though these were recorded in Scotland.

Germany, meanwhile, is suffering the brunt of Andrea today. In Bavaria, where dozens of roads are now closed, Andrea’s high winds and heavy snow have made visibility at ski resorts extremely difficult; thus, particularly at high-elevation ski resorts, where hurricane-force gusts continue, skiers have been asked to leave.

One fatality was reported today when high winds pushed a car into oncoming traffic near Regensburg (where strong winds also damaged the corrugated metal roof of a furniture market); the accident closed the A-3 highway. Train service has also been disrupted in parts of Germany.

In the north of the country, the storm brought high winds, rain, sleet, snow and storm surge, the last of which flooded the local fish market in Hamburg early this morning. Police indicated the water in Hamburg was 1.25 meters high. In Osterdeich, also in Germany’s north, downtown sidewalks were submerged in water, and in the district of Bremen Vegesack, at the mouth of the river Lesum, cars had to be pulled out of the water.

Munich, meanwhile, has experienced gusts up to 120 km/h (75 mph), as well as thunderstorms and heavy showers, according to the German Weather Service. Several trees have toppled in the city’s popular park, the English Garden; police warned people to stay out. The zoo was also closed. The German Weather Service said the storm’s high winds were expected to continue until approximately 5pm local time today, after which the worst of the winds should cease, though hurricane-force gusts and heavy snow may still be possible at higher elevations.

Elsewhere in Germany, including in Berlin, no major damage was reported. In western Austria, Andrea’s heavy winds toppled trees that blocked roads in Vorarlberg (where there was also threat of an avalanche Thursday evening, due to heavy snowfall), and in Tyrol. There was also a major power outage in Tyrol; about 10,000 households lost power Thursday night.

Despite high winds, structural damage is expected to be limited from Andrea; there have been some reports of damage to roofs, but otherwise, traffic disruptions, uprooted trees and fallen branches are the major concern throughout the region. Local officials expect most of the damage to be cleaned up in a matter of days.

Forecast

High winds and snowfall should abate over the weekend. Andrea is forecast to continue moving eastwards, decreasing in strength, and taking a similar path to the path Ulli took earlier this week.

Extratropical Cyclone Andrea
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