Severe storm XAVIER in Germany: Verification of MeteoGroup’s warnings

How well did MeteoGroup forecast the severe storm XAVIER? The cyclone hit northern Germany with gusts ranging up to 130 km/h wind speed. We look into the performance of our weather warnings, issued to the public through www.unwetterzentrale.de and our app AlertsPro.

Storm XAVIER

October 05th 2017, the severe storm XAVIER – pressure systems in Germany are named by the Freie Universität Berlin – crossed northern Germany. In a wide corridor from the German Bight to the Polish border, XAVIER’s gales reached speeds of more than 100 km/h. These severe gusts caused heavy damage, public traffic broke down and seven people were fatally injured by falling trees or branches.

From a meteorological perspective, XAVIER was a special cyclone. Its dynamics developed not like typical low-pressure systems in the mid-latitudes1, but followed the so-called Shapiro-Keyser cyclogenesis scheme2 3. Such vortexes move fastly in an overall strong atmospheric jet and involve damaging winds southwest of their centre. In case you are interested in atmospherical dynamics, I recommend having a look into the course at http://www.eumetrain.org/resources/sting_jets_2012.html.

MeteoGroup's forecasts and alerts announcing XAVIER

On Tuesday morning (October 03rd), the first weather forecasting models indicated a chance of a storm on Thursday, and our MeteoGroup forecasters started to communicate the upcoming storm risk in Germany. With each new model's results arriving, the team of www.unwetterzentrale.de sharpened the forecast and at noon the upcoming risk of gales exceeding 100 km/h was first announced.

On Wednesday morning (October 04th), we issued pre-alerts for gale-forced winds for Thursday, expected to reach peaks up to 110 km/h, starting alongside the German Bight and moving quickly towards the Southeast, crossing Hamburg around noon, and reaching Berlin in the afternoon, see http://www.wetter24.de/news/detail/2017-10-04-sturmtief-xavier-zieht-auf/. The forecasters communicated the special risks and potential impacts of the storm.

Those who started the Thursday (October 05th) with a check of our Unwetterzentrale warnings found a red alert for big areas in Northern Germany:
Screenshot from www.unwetterzentrale.de with storm alerts as active on Thursday at 07:00 CEST. Pre-alerts for the red area have been active since Wednesday morning, first active red alerts in the Northwest started the night before. The screenshot from www.unwetterzentrale.de shows storm alerts as they were in effect by Thursday at 07:00 CEST. Pre-alerts for the red area have been issued Wednesday morning, first active red alerts in the Northwest started the night before. Red alerts announce that gusts of more than 100 km/h speed are to be expected.

Did our forecasts and warnings hit the nail?

To warn as little as possible but as often and intensively as needed is a challenging tightrope walk. Intensive atmospheric phenomena like thunderstorms or a Keyser-Shapiro cyclone include sub-scale dynamics and chaotic behaviour. The development cannot be forecasted exactly, but only in terms of ‘probability’, ‘chance’ and ‘risk’. We want to warn all people which might potentially be impacted by the storm. On the other hand, when we warn too frequently of storms which end up not hitting a warned user, the awareness will dilute.

At MeteoGroup, we measure the quality of our severe weather warnings, issued by www.unwetterzentrale.de, on a daily basis. This allows us to provide immediate quality feedback to our forecasters. We can learn from failures and celebrate our forecasting successes. More information on MeteoGroup’s verification of severe weather events can be found at https://www.researchgate.net/publication/319313555_Operational_user-centric_verification_of_severe_weather_warnings.

Below, I compare the warnings in effect on Thursday 07:00 CEST (left) to the highest observed wind speed (right). The dots and flags indicate weather stations reporting gusts, either operated by the German national weather service DWD (primary and secondary network, a total of 300 stations in Germany) or operated by MeteoGroup. The MeteoGroup-owned station network includes 467 stations in Germany reporting wind gusts.

MeteoGroup warnings as active on Thursday 07:00 CEST (left) and observed highest wind gust on Thursday 05 October 2017(right)

Red flags show, where on Thursday stations reported gales between 100 km/h and 130 km/h, which corresponds to our red warn level. Orange dots mark stations where gusts between 75 km/h and 100 km/h have been observed. This range corresponds with our orange level for gust warnings. Green dots mark stations which measured only windspeeds below 75 km/h.

Even a handful of violet flags can be spotted, all on very exposed stations. The leader is the Brocken mountaintop, 1134 metres above sea level, where 177 km/h have been measured.

The warnings of www.unwetterzentrale.de excellently cover the gusts as observed on Thursday. Southwest of XAVIER’s track, for a ribbon of ~100-150 km width, the wind did not reach a red level. Given the extraordinary strength of the cyclone and the involved risks we consider this over-warning as acceptable. MeteoGroup’s early announcement of the storm, the communication of uncertainty, and, finally, the alerts issued in good time to prepare proper mitigation can be considered as exemplary.

MeteoGroup’s support for insurance claims

We use the gust reports from more than 750 observing stations, operated in Germany by the DWD and by MeteoGroup itself, for a storm field analysis. The observation data, radar information and high-quality atmospheric models are combined to provide a high resolution grid or spatial shapes of the daily maximum gusts in storm fields. The results are accessible for private persons via www.meteoarchiv.de; insurance companies either use a direct access via website or ingest the data into their own systems.

For storm XAVIER the MeteoGroup storm field analysis results in this pattern:
Result of MeteoGroup's storm field analysis for October 05th 2017

Gusts above 100 km/h as observed on Thursday 05 October 2017

The below table lists all gusts above 100 km/h as observed by DWD stations or MeteoGroup owned stations on October 05th 2017:

Station-ID Max gust 05 Oct 2017 Station name Latitude N Longitude E Elevation m above NN
10453 177 Brocken 51.7986 10.6183 1134
6510390 136 Berlin-Wannsee (exposed location) 52.4312 13.1842 40
10578 135 Fichtelberg 50.4283 12.9535 1213
6510452 132 Braunlage-Wurmberg 51.75 10.6167 965
6510474 131 Dessau-Rosslau 51.8337 12.1822 57
6510593 131 Ebersbach (Oberlausitz) 51.0097 14.5682 400
6510347 123 Braunschweig Flughafen 52.3163 10.5647 86
10476 122 Holzdorf (Flugplatz) 51.7657 13.1667 81
3010371 122 Berge 52.6198 12.7867 40
3010123 120 Spiekeroog 53.7667 7.6667 14
10396 119 Manschnow 52.5467 14.5453 13
6510339 119 Hannover-Messe 52.3242 9.7997 73
10385 118 Berlin-Schönefeld 52.3807 13.5307 46
6510373 118 Nauen 52.5978 12.8407 41
10393 117 Lindenberg 52.2085 14.118 98
10113 117 Norderney 53.7123 7.1518 11
6510114 117 Baltrum 53.7297 7.3743 5
6510226 117 Syke 52.9125 8.8258 50
6510387 115 Berlin-Adlershof 52.4328 13.5375 40
10376 115 Baruth 52.0613 13.4997 56
6510248 115 Uelzen 52.9908 10.6732 68
6510594 115 Hochwald 50.8225 14.7263 749
10365 114 Genthin 52.3875 12.16 38
10338 114 Hannover 52.4643 9.6778 55
10961 113 Zugspitze 47.4208 10.9847 2964
6510116 113 Esens-Bensersiel 53.6753 7.5693 10
3010145 113 Ruthenstrom 53.7167 9.4167 7
3010391 113 Heckelberg 52.7462 13.8427 82
6510112 113 Juist-Flugplatz 53.6807 7.0578 3
6510014 112 Helgoland-Oberland 54.1868 7.8753 53
6510120 112 Wangerooge 53.7847 7.8528 4
6510127 112 Wilhelmshaven (MeteoGroup) 53.5147 8.1463 1
10381 112 Berlin-Dahlem (FU) 52.4537 13.3017 51
3010341 112 Süpplingen 52.2167 10.8333 129
10382 111 Berlin/Tegel 52.5643 13.3088 37
6510376 111 Luckenwalde 52.0893 13.1837 46
6510896 111 Falkenstein 49.085 13.2807 1308
10379 111 Potsdam 52.3822 13.0622 81
6510167 111 Luebz 53.4775 12.0258 70
6510363 110 Barleben 52.1818 11.5982 40
10384 109 Berlin/Tempelhof 52.4675 13.4018 49
6510115 109 Langeoog 53.7432 7.4917 2
6510126 109 Harlesiel-Flugplatz 53.7063 7.8193 2
6510976 109 Wallberg 47.6613 11.7937 1620
10289 109 Grünow 53.3153 13.9338 57
10791 109 Großer Arber 49.113 13.1342 1436
6510145 109 Hamburg-Veddel 53.5112 10.0457 7
10334 108 Wunstorf 52.4605 9.4312 57
10335 108 Bückeburg 52.2817 9.0888 68
6510319 108 Emstek 52.815 8.1938 55
10261 107 Seehausen 52.8912 11.7297 21
6510429 107 Bueren-Ahden 51.6113 8.6222 213
6510998 107 St. Bartholom/Koenigssee 47.5438 12.9725 605
10724 106 Weinbiet 49.3758 8.1214 553
6510128 106 Butjadingen 53.5828 8.3687 1
3010395 106 Müncheberg 52.5177 14.1232 63
6510113 106 Norden-Norddeich 53.6188 7.1533 2
6510117 106 Neuharlingersiel 53.6957 7.69 2
6510227 105 Verden 52.9193 9.2307 22
6510352 105 Wolfsburg 52.4688 10.7975 81
6510195 105 Penkun (Vorpommern) 53.3012 14.2393 29
6510494 105 Mattendorf 51.6667 14.5567 98
6510236 104 Bad Fallingbostel 52.8693 9.7043 37
6510351 104 Wolfsburg-Autostadt 52.4325 10.7972 60
6510395 104 Rietz Neuendorf 52.2263 14.1762 80
10235 104 Soltau 52.9603 9.7932 77
10490 104 Doberlug/Kirchhain 51.645 13.5747 98
10270 103 Neuruppin 52.9037 12.8072 38
6510205 103 Aurich 53.4763 7.6262 10
6510463 103 Stassfurt 51.8593 11.5778 72
10348 103 Braunschweig 52.2913 10.4463 82
3110216 103 Brake 53.3167 8.46667 1
6510455 103 Halberstadt 51.9007 11.0575 113
10496 102 Cottbus 51.7762 14.3168 70
3010269 102 Rechlin 53.3167 12.7167 62
10368 102 Wiesenburg 52.1207 12.4587 188
6510016 102 Sylt-List 55.0375 8.3882 20
6510110 102 Borkum (MeteoGroup) 53.5843 6.6607 2
6510358 102 Haldensleben 52.3038 11.4242 82
6510437 102 Beverungen-Drenke 51.6758 9.3133 242
6510484 102 Kabelsketal 51.4438 12.1343 126
3010378 101 Brandenburg/Havel 52.4167 12.5667 31
3010476 101 Langenlipsdorf 51.9173 13.0878 91
10147 101 Hamburg-Fuhlsbüttel 53.6332 9.9882 11
10224 101 Bremen 53.045 8.7978 4
10126 101 Wittmund 53.55 7.6667 12
10343 101 Celle 52.5958 10.0297 39
6510475 101 Jessen 51.7908 12.9518 75
10200 100 Emden 53.3882 7.2287 0
3010143 100 Travemünde 53.95 10.8833 2
10131 100 Cuxhaven 53.8714 8.7058 5
10427 100 Kahler Asten 51.1803 8.4892 839
6510131 100 Otterndorf 53.825 8.8872 1
6510223 100 Osterholz-Scharmbeck 53.2297 8.7908 34
  1. See Bjerknes, J., and H. Solberg, 1921: Meteorological conditions for the formation of rain. Geofys. Publ., 2(3), 3-61.

  2. See Shapiro, M.A., and D. Keyser, 1990: Fronts, jet streams and the tropopause. Extratropical Cyclones: The Erik Palmen Memorial Volume, C. W. Newton and E. O. Holopainen, Eds., Amer. Meteor. Soc., 167-191.

  3. See Shapiro, M.A., and Coauthors, 1999: A planetary-scale to mesoscale perspective of the life cycles of extratropical cyclones: The bridge between theory and observations. The Life Cycles of Extratropical Cyclones, M. A. Shapiro and S. Gronas, Eds., Amer. Meteor. Soc., 139- 185.

Evelyn Müller

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