Severe Storm XAVER Across Northern Europe from 5 to 7 December 2013 Dr

Severe storm XAVER across northern Europe from 5 to 7 December 2013 Dr. Thomas Deutschländer, Karsten Friedrich, Dr. Susanne Haeseler, Christiana Lefebvre; updated: 30 December 2013

Introduction

Severe storm XAVER, moving across northern Europe in early December (Fig. 1), caused severe winds with gusts of hurricane force across northern Germany and at higher sites. Schools and some Christmas markets were closed as a precaution. Shipping and rail traffic was shut down in places and flights were cancelled. In the area of the German Bight, several consecutive storm surges occurred due to winds from the northwest. Hallig lowlands were flooded. On the islands, dunes broke off and sand was eroded. After the passing of the cold front of the severe storm, soft hail and snow showers occurred, leading to dangerous street conditions and road accidents. It became wintry for a short time with snow even at lower sites.

Fig. 1: Track of XAVER over Europe from 4 to 7 December 2013. [Source: DWD]

Other XAVER-affected countries reported similar impacts as Germany. Hemsby in Norfolk on the eastern coast of England was seriously struck, when several cliff-top houses disappeared into the sea as the high tide eroded the cliff below. More than 10 people died Europe-wide due to the storm.

Development of XAVER

On 4 December 2013, a low formed from a warm front wave over the North Atlantic south of Greenland. It rapidly strengthened to a severe storm during the night to the 5th of December and on the 5th (Fig. 2a and 2b) known under the name of XAVER.

On its way across southern Sweden, a squall line in connection with the cold front of the storm reached north-western Germany in the afternoon of 5 December, at which hurricane force gusts occurred (Fig. 2b).

Severe storm XAVER reached its peak development on the 5th at 18 UTC with a central pressure of 960 hPa. Then it moved only slowly eastwards.

In the maritime Arctic air introduced on the rear side of the cold front rainfall occurred, merg- ing into snow even in the lowland (Fig. 2c, 3 and 4). Severe snow drifts occurred in parts of the highland.

Fig. 2a: Surface analysis North Atlantic/Europe on 5 December 2013, 00 UTC. [Source: DWD]

Fig. 2b: Surface analysis North Atlantic/Europe on 5 December 2013, 18 UTC. [Source: DWD]

Fig. 2c: Surface analysis North Atlantic/Europe on 6 December 2013, 00 UTC. [Source: DWD]

Fig. 3: Satellite image of northern Europe with air pressure (in hPa) and wind (direction and speed) on 6 December 2013, 00 UTC. [Source: DWD]

Fig. 4: Satellite image of Europe on 6 December 2013, 06 UTC. [Source: DWD]

While on 6 December the centre of XAVER moved towards the Baltic, the winds at the Ger- man coasts still blew with storm force.

Mean winds and peak gusts in Germany

The peak gusts reached between 150 and 160 km/h on 5th/6th December, i.e. hurricane force (Fig. 5). Glücksburg/Meierwik recorded a peak gust of 44 m/s (158.4 km/h) on the 6th.

Fig. 5: Peak gusts (in km/h) in northern Germany and surrounding countries. [Source: DWD] Top: on 5 December 2013 between 12 and 18 UTC. Bottom: on 6 December 2013 between 00 and 06 UTC.

On the evening of the 5th, 10-minute sustained winds of 103 km/h and more were recorded, especially on the North Frisian coast (Fig. 6). This meant a wind force of Bft 11 (103 to 117 km/h; violent storm), locally even Bft 12 (≥ 118 km/h; hurricane). At that time, the centre of the storm was located over southern Sweden.

Fig. 6: 10-minute sustained winds (in km/h) on 5 December 2013, 19 UTC. [Source: DWD]

Table 1 shows the maximum wind speeds (peak gusts and 10-minute sustained) on 5 to 7 December 2013. Severe storm XAVER caused high wind speeds in the area of the North Sea not as high as in severe storm CHRISTIAN, which crossed northern Germany at the end of October.

6 5 Dec. 2013 6 Dec. 2013 7 Dec. 2013 max. max. max. peak gust sustained wind peak gust sustained wind peak gust sustained wind station km/h km/h km/h km/h km/h km/h Brocken 153.0 128.9 131.4 96.1 95.4 71.3 List auf Sylt 148.3 103.0 129.2 99.7 90.4 70.2 Spiekeroog (SWN) 148.0 130.3 90.4 Leuchtturm Kiel 145.8 99.4 137.2 108.7 82.4 65.9 Strucklahnungshörn 141.5 130.0 83.9 Fichtelberg 140.4 103.0 145.1 100.8 111.2 81.0 Büsum 136.4 122.8 87.5 Rostock-Warnemünde 135.7 96.5 114.8 90.4 78.8 65.9 UFS Deutsche Bucht 135.7 101.5 83.9 67.7 Hallig Hooge 134.6 118.4 88.6 Fehmarn 131.8 94.0 125.3 94.7 85.0 67.7 Putlos 126.4 110.9 84.6 Helgoland 126.0 90.7 112.0 79.9 85.3 56.9 Bremerhaven 125.3 92.9 109.4 81.0 94.0 64.8 Schönhagen (Ostseebad) 122.4 69.8 108.7 65.5 55.8 37.1 Elpersbüttel 121.7 85.0 120.6 79.2 70.6 50.8 Norderney 121.7 96.1 117.7 90.7 87.5 64.8 Feldberg/Schwarzwald 121.3 99.0 101.5 70.9 53.6 41.4 Boltenhagen 121.0 76.3 100.8 71.6 68.0 50.0 Darßer Ort (SWN) 121.0 120.6 78.8 Arkona 119.5 97.6 124.9 99.4 91.8 64.1 Leck 119.2 77.0 111.2 75.2 70.2 41.8 Greifswalder Oie 118.4 93.2 129.6 98.6 82.8 67.0 Bastorf-Kägsdorf (SWN) 118.1 113.8 83.9 Schleswig 118.1 64.4 97.6 58.7 49.0 27.0 Schwerin 112.7 56.5 86.8 50.4 51.5 32.0 Flensburg (Schäferhaus) 112.3 96.5 45.4 Cuxhaven 111.6 77.0 104.4 74.5 77.0 59.0 Emden 110.9 69.1 105.5 71.6 54.4 35.3 Kahler Asten 110.9 73.4 97.6 64.1 64.4 46.1 Borkum-Süderstraße 109.1 126.4 57.2 Bremervörde 107.6 58.7 84.6 46.1 60.1 34.6 Chieming 107.6 76.0 88.9 59.4 61.6 41.0 Weinbiet 107.6 76.0 80.3 54.7 65.2 48.2 Stötten 106.9 76.0 81.7 61.2 54.7 39.6 Groß Lüsewitz 105.8 65.9 96.1 63.4 68.4 45.0 Barth 103.3 64.8 99.7 68.8 65.5 44.6 Travemünde 103.0 120.2 57.6 Hohenpeißenberg 100.4 53.3 88.9 51.8 58.0 29.5 Ueckermünde 100.1 56.5 88.2 51.5 54.0 34.6 Dresden-Klotzsche 99.4 59.4 83.5 57.6 67.7 45.0 Hamburg-Fuhlsbüttel 99.4 59.8 97.6 59.8 50.0 30.6 Tab. 1: Peak gusts and 10-minute sustained wind speeds. [Source: DWD]

Figure 7a shows the development of the highest gusts within 10-minute intervals at the 3 stations List/Sylt, Norderney and Rostock-Warnemünde.

Fig. 7a: Development of peak gusts from 10-minute intervals (in km/h) at 3 weather stations from 5 to 8 December 2013. [Source: DWD]

Figure 7b shows the development of the 10-minute sustained wind speed at the 3 stations List/Sylt, Norderney and Rostock-Warnemünde.

Fig. 7b: Development of 10-minute sustained wind speeds (in km/h) at 3 weather stations from 5 to 8 December 2013. [Source: DWD] 8

In the Baltic Sea, the sustained wind speed remained below gale force till the afternoon of 5 December. With passage of the cold front, the wind in the Baltic Sea increased remarkably and reached the force that prevailed in the North Sea since the early afternoon. Notable are the sustained high wind speeds, persisting during the 6th and weakening only by late afternoon and in the evening of 7 December in the Baltic Sea. The wind speed showed noticeable variations of intensity due to high atmospheric instability.

The development of the wind speed at Hamburg-St. Pauli illustrates the high variability of the wind field very well (Fig. 8).

Fig. 8: Development of wind speed (in knots) and air pressure (in hPa) at Hamburg-St. Pauli on 5 December 2013. There were some data outages. [Source: DWD]

The development of the wind direction in Figure 9 shows the clear turn from southwest to northwest associated with the cold front passage in the afternoon of 5 December. In the Bal- tic Sea, the wind turned at first to the west and then in the course of 6 December to northwest. Different from the North Sea, it kept this wind direction until the end of 7 December.

Fig. 9: Development of wind direction (in degree) at 3 weather stations from 5 to 8 December 2013. [Source: DWD]

Sea state

Severe storm XAVER triggered waves of more than 8 metres, especially in the German Bight and off the Polish eastern coast (Fig. 10a, 10b and 11).

Fig. 10a: Wind (arrows), wave height (coloured in metre) and air pressure (lines in hPa) in the area of the North Sea on 6 December 2013, 00 UTC. [Source: DWD]

Fig. 10b: Wind (arrows), wave height (coloured in metre) and air pressure (lines in hPa) in the area of the Baltic Sea on 6 December 2013, 00 UTC. [Source: DWD]

Fig. 11: Weeklong time series of sea state measurements at the station Außenelbe in the German Bight from 2 to 9 December 2013. [Source: BSH]

Water levels, storm surge and low water

Unlike severe storm CHRISTIAN on 28 October 2013, which passed rapidly and therefore influencing the water levels of North Sea and Baltic Sea only marginally, severe storm XAVER affected them significantly. But the change of the water levels at the North Sea and the Baltic Sea was very different. In addition to the wind direction, it was also the luminary constellation that affected the water level, because it was new moon on 3 December. That means that sun, moon and earth were almost in line, and by this tidal force the high tide was higher than usual (spring tide). While islands, coasts and lower stream courses, draining to the North Sea, experienced several consecutive, partly heavy to severe storm surges, a strik- ing low water event occurred at the Baltic Sea as a start.

In the morning of 5 December, the wind across the North Sea and the Baltic Sea blew from south-westerly to westerly directions. This caused a severe storm surge in the North Frisian insular and coastal region already in the afternoon, when the water level at Husum rose nearly 3 m above the mean high tide (MThw) (Fig. 12). After the passage of the cold front and the successive wind convergences, the wind in the North Sea turned to northwest in the late afternoon hours while getting stronger. The gusts often reached hurricane force and the 10-minute sustained winds a strength of Bft 10 to 11. Due to the spring tide and the change of wind direction, the low water level in the evening, occurring between about 7 p.m. local time in East Frisia and 10 p.m. local time in North Frisia, was well above average within the range of the mean high tide (MThw). The persistent strong wind and the long fetch on the rear side of the low, relocating across southern Sweden to the central Baltic Sea, caused an extreme subsequent high tide. During this high tide, occurring along the German North Sea coast at 1 a.m. of 6 December, the water levels from 2.50 to nearly 4 m above high tide partly exceeded those of the last extreme storm surge on 1 November 2006 (storm surge caused by severe storm BRITTA). The subsequent low tide in the morning was similarly high like the one before. The following high tide on the afternoon of 6 December was once again well above average, but it did not reach the peak of the previous day. On 7 December, the water levels were within the range of the mean water levels.

Fig. 12: Water levels at the North Sea (in cm) from 5 to 8 December 2013. MThw = mean high tide; MTnw = mean low tide. [Data Source: WSV, Pegelonline]

In contrast, the wind direction at the Baltic Sea remained west till the morning of 6 December (Fig. 9), while the wind force increased to 10 to 11 Bft (partly to 12 Bft). This led to low water along the whole German Baltic Sea coast. According to a report of the BSH, the water level at the Flensburg Firth was particularly low. At Flensburg, an anomaly of -2.08 m from the mean water level was recorded (Fig. 13). The remaining coastal areas experienced a water level decrease to 1.5 to 2.0 m below the mean water level with lowest values being recorded in the morning of 6 December. Then the wind turned to northwest there as well. The water levels rose as well, but they remained below the mean high waters. Different to the North Sea, the north-westerly wind persisted till the early night of 8 December over the Baltic Sea.

12 So the water levels, after peaking between about 2 and 5 a.m. on 7 December, remained above the mean water level till the afternoon of the next day.

Fig. 13: Water levels at the Baltic Sea (in cm) from 5 to 8 December 2013. MHW = mean high water; MNW = mean low water. [Data source: WSV, Pegelonline]

For further information see special reports published by the Bundesamt für Seeschifffahrt und Hydrographie (BSH) (see chapter „Sources and further information“).

At Hamburg-St. Pauli, the water level rose to about 811 cm on the morning of 5 December (Fig. 14). This is about 1 m above the mean high tide (MThw). The evening water level reached 936 cm. On the morning of 6 December, Hamburg experienced a very severe storm surge with a peak water level of 1109 cm, i.e. 3.98 m above the mean high tide. Even if the evening high water level of 1000 cm was slightly lower, it was a severe storm surge.

Fig. 14: Water level on the Elbe at Hamburg-St. Pauli from 5 to 8 December 2013. MThw = mean high tide; MTnw = mean low tide. [Data source: WSV, Pegelonline]

The storm surge on the morning of 6 Decembers 2013 in Hamburg-St. Pauli with 3.98 m above MThw was among the 5 highest measured at this location in over 100 years. The highest was recorded in 1976 with 4.67 m above MThw, followed by a storm surge in 1962 with 4.03 m above MThw as well as two storm surges in 1994 and 1995 with 3.98 m and 3.99 m above MThw, respectively.

13 Precipitation in Germany

Severe storm XAVER caused regional precipitation totals of more than 10 mm (Fig. 15).

Fig. 15: Daily precipitation (in mm) for Ger- many on 5 December 2013. Preliminary values, unchecked. [Source: DWD]

In the Arctic air on the rear side of XAVER, heavy snow and soft hail showers occurred even at lower sites. Snow depths of about 5 to 10 cm were reported from the highlands. The exposed weather station on the Brocken even recorded about 50 cm of fresh snow. Figure 16 shows the snow depths on the mornings of 6 and 7 December.

Fig. 16: Snow depths (in cm) over northern Germany. FL = spots. [Source: DWD] Top: on 6 December 2013, 06 UTC. Bottom: on 7 December 2013, 06 UTC.

Climatological classification of XAVER

For a climatological classification, the 10-minute sustained wind speeds on the Brocken, the highest peak of the Harz mountain range, for different storm events of the last years are compared in Figure 17. In each case a 3-day period is shown. Among the shown storm events, severe storm KYRILL has caused the highest wind speeds on the Brocken and also its duration was much longer than that of XAVER. Also severe storm LOTHAR caused higher wind speeds on the Brocken than XAVER and caused with wind speeds of 30 to 40 m/s for several hours after the peak winds occurred. The peak wind speeds during EMMA were not as high, but it also persisted for more than 2 days.

Fig. 17: Comparison of storm events over a 3-day period. [Source: DWD]

A classification of severe storm XAVER against the background of climate change is pretty difficult. Some regional climate projections suggest that the number of winter storms in Ger- many may possibly increase by up to 50 % in the course of the 21st century. But the credibil- ity of this statement is low, because other climate models do not reinforce it. For example: At this time, it is hardly possible to say whether the entire country of Germany will be affected or if individual regions could possibly be struck harder than others. Besides, it is impossible to gather information about long-range climate changes from an individual event like XAVER. Only if a change in the frequency or intensity of such storm is observed for many years, can it really be assumed to be a reliable trend. To attribute a statistically detected trend to human activities is even more problematic. Responsible for this is the fact that natural climate variations can superimpose the impacts of human-induced greenhouse effect. They originate, among others, from the time-varying solar activity and the periodic variations of the global ocean circulation.

Analyses of the sustained and the maximum wind speed in the German Bight area for the period from 1880 to 2012 show variations with a period of about 40 years. The development of sustained and maximum wind speed is practically parallel. A trend, however, is seen in neither of the two time series. The anticipated future trend cannot be verified so far. Also the fact that storm CHRISTIAN which raged across Germany only a few weeks before XAVER, is to be regarded as normal from a climatological point of view because winter storms often appear in clusters. This is due to the position and intensity of the so-called frontal zone, i.e. the air mass boundary between warm air from the area of the sub-tropics and cold polar air. If this boundary is well developed and if Central Europe is located in its area, then repeated storm events occur in many years. During the winter of 1989/1990, for example, altogether 8 severe storms occurred from 25 January to 1 March. Then the storms VIVIAN and WIEBCKE induced altogether 5 storm surges within only 3 days in quick succession. The impacts of XAVER are comparable with the situation in the year 1990, even though there were 2 severe storms at that time.

16 Reports and data of other European weather services

United Kingdom (UK)

XAVER caused storm force winds mainly in the north of the UK. Across Scotland and northern parts of England, widespread gusts of between 96 and 129 km/h (60 and 80 mph) occurred on the 4th/5th December. Some very high level mountain sites have reported wind speeds of over 225 km/h (140 mph), but these are in very exposed areas and not repre- sentative of the winds most people have experienced (Met Office).

A tidal surge was triggered on the east coast, being the most serious one in over 60 years (Environment Agency). In some places sea levels were higher than those during the devas- tating floods of January 1953.

Netherlands

Large parts of the Netherlands experienced the strongest winds of the storm in the afternoon and the early evening of 5 December with a squall line active in Germany as well. In the north and on the western coasts, gusts of 110 to 137 km/h were recorded with the peak gust at the weather station Stavoren. Over the remaining parts of the country, gusts of 75 to 100 km/h occurred.

Denmark

In Denmark, the severe storm was named BODIL. On 5 December, it caused gusts from storm force (Bft 10) to hurricane force (Bft 12) in the whole country. The maximum 10-minute sustained wind speeds were between 54 and 108 km/h (15 to 30 m/s) with regionally higher values. The strongest winds blew in the afternoon at the Nissum Fjord, an inlet located in West Jutland. There the maximum 10-minute sustained wind was 132 km/h (36.6 m/s), and the peak gust 159 km/h (44.2 m/s).

Norway

The Norwegian station Eigeroya (Island at the south coast of Norway) recorded a 10-minute sustained wind speed of 129.6 km/h (36 m/s) on 5 December 2013 at 15 UTC. At the same station, peak gusts of 169 km/h (47 m/s) occurred.

Sweden

In Sweden, XAVER is known under the name of SVEN. At the stations Nidingen and Väder- öarna, at/off the west coast of southern Sweden, peak gusts of 144 km/h (40 m/s) occurred on the 5th/6th December. The maximum sustained wind speed recorded at Väderöarna was 108 km/h (30 m/s).

The storm caused new local water level records on the Öresund on 6 December. Several monitoring points recorded levels of more than 150 cm above the mean water level.

Poland

In Poland, XAVER is vernacularly called KSAVERY. At the weather station Sniezka (Schneekoppe), on the border between Poland and the Czech Republic at a height of about 1600 m, 10-minute sustained wind speeds of 137 km/h (38 m/s) were reported on

17 6 December 2013 at 00 and 06 UTC. The coastal station Ustka reported a mean wind speed of 86 km/h (24 m/s) on 6 December at 14 UTC.

Sources and further information

. Bundesamt für Seeschifffahrt und Hydrographie (BSH): Seegang. http://www.bsh.de/de/Meeresdaten/Beobachtungen/Seegang/index.jsp . Bundesamt für Seeschifffahrt und Hydrographie (BSH): Wasserstand. http://www.bsh.de/aktdat/wvd/wahome.htm . Bundesamt für Seeschifffahrt und Hydrographie (BSH): Die Nordseesturmfluten vom 5. und 6.12.2013. http://www.bsh.de/de/Meeresdaten/Vorhersagen/Sturmfluten/Berichte/Sturmflut_5- 6_12_2013.pdf . Bundesamt für Seeschifffahrt und Hydrographie (BSH): Niedrigwasser vom 06.12.2013. http://www.bsh.de/de/Meeresdaten/Vorhersagen/Sturmfluten/Berichte/niedrigwasser_ostse e_06_12_2013.pdf . Bundesamt für Seeschifffahrt und Hydrographie (BSH): Sturmflut vom 07.12.2013. http://www.bsh.de/de/Meeresdaten/Vorhersagen/Sturmfluten/Berichte/Sturmflut_ostsee_07 _12_2013.pdf . Danmarks Meteorologiske Institut (DMI): Status på stormen Bodil. http://www.dmi.dk/nyheder/arkiv/nyheder-2013/12/status-paa-bodil/ . Danmarks Meteorologiske Institut (DMI): Bodil har toppet. http://www.dmi.dk/nyheder/arkiv/nyheder-2013/12/bodil-har-toppet/ . Danmarks Meteorologiske Institut (DMI): Langvarige Bodil klassificeret som ´orkanlignende´. http://www.dmi.dk/nyheder/arkiv/nyheder-2013/12/bodil-klassificeret-som-orkanlignende/ . Danmarks Meteorologiske Institut (DMI): Bodil og det beskidte dusin. http://www.dmi.dk/nyheder/arkiv/nyheder-2013/12/bodil-og-det-beskidte-dusin/ . Deutscher Wetterdienst (DWD): Data archive. . Deutscher Wetterdienst (DWD): Heavy storm CHRISTIAN on 28 October 2013. . Deutscher Wetterdienst (DWD): Thema des Tages vom 4. bis 8. Dezember 2013. . Environment Agency, UK: 1953 East Coast floods. http://www.environment-agency.gov.uk/homeandleisure/floods/145351.aspx . Environment Agency, UK (07-Dec-2013): Warnings lifted after most serious tidal surge in over 60 years. http://www.environment- agency.gov.uk/news/151103.aspx?month=12&year=2013§or=Flood . Environment Agency, UK (10-Dec-2013): Thames Barrier stands up to its biggest ever tide. http://www.environment- agency.gov.uk/news/151138.aspx?month=12&year=2013§or=Flood . Koninklijk Nederlands Meteorologisch Instituut (KNMI): De zware storm van vijf december. http://www.knmi.nl/cms/content/117153/de_zware_storm_van_vijf_december . Koninklijk Nederlands Meteorologisch Instituut (KNMI): Klimadata en –advies. Zware storm op 5 december. http://www.knmi.nl/klimatologie/storm_dec13.html . Met Office, UK (5 December 2013): An Atlantic storm has tracked east to the north of Scot- land overnight, bringing very strong winds across northern parts of the UK. http://www.metoffice.gov.uk/news/releases/archive/2013/storm-surge . Met Office, UK (5 December 2013): Updated: Wind and rainfall data 4 to 5 December 2013. http://metofficenews.wordpress.com/2013/12/05/overnight-wind-and-rainfall-data-4-to-5- december-2013/ . Niedersächsischer Landesbetrieb für Wasserwirtschaft, Küsten- und Naturschutz (NLWKN): Sturmflutgefahr an der Küste und auf den Inseln. Zwei Meter über dem norma- len Hochwasser in der Nacht zum Freitag möglich // Presseinformation vom 29. November 2013.

18 http://www.nlwkn.niedersachsen.de/aktuelles/pressemitteilungen/sturmflutgefahr-an-der- kueste-und-auf-den-inseln-120187.html . Sveriges meteorologiska och hydrologiska institut (SMHI): Sven var förhållandevis extremast vid Bohuskusten. (06 december 2013) http://www.smhi.se/nyhetsarkiv/sven-var-forhallandevis-extremast-vid-bohuskusten- 1.34671?search=yes&month=12&year=2013 . Sveriges meteorologiska och hydrologiska institut (SMHI): Stormen Sven gav nya vat- tenståndsrekord i Öresund. (10 december 2013) http://www.smhi.se/nyhetsarkiv/stormen-sven-gav-nya-vattenstandsrekord-i-oresund- 1.34732?search=yes&month=12&year=2013 . Sveriges meteorologiska och hydrologiska institut (SMHI): Väderhändelser imängd. (30 december 2013) http://www.smhi.se/nyhetsarkiv/handelserik-julmanad- 1.35164?search=yes&month=12&year=2013 . Wasser- und Schifffahrtsverwaltung des Bundes (WSV): Pegelonline. http://www.pegelonline.wsv.de/gast/start