The Devastating Western European Winter Storm 27-28 February 2010 By Richard H. Grumm National Weather Service 1. INTRODUCTION A strong late winter storm, called Xynthia 1, raced across Western Europe the 27 th and 28 th of February 2010 (Fig. 1). The storm was over the eastern Atlantic at 0000 UTC, west of Portugal before moving onshore around 1200 UTC on 27 February, and then moved across the Bay of Biscay before moving into France around 0000 UTC on 28 February. By 0000 UTC 1 March 2010 the storm was over the western Baltic Sea (Fig. 1i). The storm claimed the lives of around 62 people as it moved across Western Europe. Most of the deaths were near La Rochelle, France where strong winds, early spring high tide, and a storm surge caused a rapid rise in water. The majority of the deaths were due to drowning. There were 51 reported deaths in France and an additional 11 deaths were reported in Western Europe, primarily in Belgium, Germany, Spain and Portugal. The storm caused flooding and two flood related fatalities in the Azores. A breached sea wall along the French coast near the town of L Aiguillon-sur-Mer was the cause of most of the reported fatalities. The storm produced heavy rains and high winds causing airports to close, delayed rail traffic, and caused widespread power failures. Hurricane force winds were reported along the Atlantic Coast of France flooding low lying coastal areas. The storm destroyed homes and downed power lines. As many as 1 million homes in France may have suffered power outages due to the storm. The airports around Paris were closed for several hours during the relatively well predicted storm. This paper will document the conditions associated with this tragic event. The focus here is on the pattern and the anomalies of key features 1 Boston Herald report. which facilitate identifying such events. A mix of model and re-analysis data is used to present the case. 2. METHODS AND DATA The 500 hpa heights, 850 hpa temperatures and winds, other standard level fields were derived from the Japanese reanalysis data using the climatology from the NCEP/NCAR (Kalnay et al. 1996) reanalysis data to compute the departures of the large scale fields from normal. Thus, all the means and standard deviations used to compute the standardized anomalies were from the NCEP/NCAR data as described by Hart and Grumm (2001). Anomalies were displayed in standard deviations from normal, as standardized anomalies. All data were displayed using GrADS (Doty and Kinter 1995). The standardized anomalies computed as: SD = (F M)/σ ( ) Where F is the value from the reanalysis data at each grid point, M is the mean for the specified date and time at each grid point and σ is the value of 1 standard deviation at each grid point. Model and ensemble data shown here were primarily limited to the GFS and GEFS. The 1.25x1.25 degree JMA data may be used when it becomes available. The NAM and SREF data were also available for use in this study. Displays will focus on the observed pattern and some forecast issues associated with the pattern. For brevity, times will be displayed in day and hour format such at 28/0000 UTC signifies 28 February 2010 at 0000 UTC. 3. RESULTS
Figure 1. GFS 00-hour analysis of mean sea level pressure (hpa) and anomalies over Europe valid at a) 0000 UTC 27 February, b) 0600 UTC 27 February, c) 1200 UTC 27 February, d) 1800 UTC 27 February, e) 0000 UTC 28 February, f) 0600 UTC 28 February, g) 1200 UTC 28 February, h) 1800 UTC 28 February, and i) 0000 UTC 01 March i. Synoptic scale pattern The large scale pattern over the Atlantic Basin is shown in Figure 2-4. These data show the 500 hpa heights, 250 hpa winds, and precipitable water (PW) in 6-hour increments as the storm moved inland. Key features include the deep 500 hpa trough (Fig. 2) which was off the Iberian Peninsula at 27/0000 UTC with -3 to -4SD height anomalies. A strong 500 hpa ridge was present over North Africa with +2 to +3 SD height anomalies. Another large ridge and trough were present over the western Atlantic. The 250 hpa winds (Fig. 3) showed a strong westerly jet over Western Europe at 27/0000 UTC with +3SD anomalies in the winds. There was an implied jet entrance region over the eastern Atlantic where the cyclone was developing. Initially, the jet had a nice banana jet appearance to it. The shape was potentially related to the height gradient and the push of the system over the large North African ridge. A second jet streak was present moving about the 500 hpa
Figure 2. As in Figure 1 except over the Atlantic Basin showing 500 hpa heights and anomalies. trough. This created a coupled jet appearance in the wind field (Figs. 3b-d). In addition to the strong jet and the deep trough, the system was ingesting warm moist air. A surge of high PW (Fig. 4) was clearly visible moving from the tropical Atlantic into the Iberian Peninsula. PW anomalies of 2 to 4SDs above normal were within this plume of moist air. A few locations saw PW anomalies in excess of +5SDs above normal indicating a rich source of moisture into the storm system. ii. Regional pattern and anomalies The pressure field and the surface cyclone were shown in Figure 1. The key pressure feature was the deep cyclone. The strong gradient ahead of the cyclone produced strong southerly winds (Fig. 5) and allowed a surge of warm air to move into Europe ahead of the advancing cyclone (Fig. 6). The 850 hpa winds and v-wind anomalies (Fig. 5) showed that there was a broad band of +3 to +4SD southerly winds. Within this band, the 850 hpa v-winds achieved some +5 and +6SD wind
anomalies suggesting well above southerly winds over the region. This implied an intense cyclone and winds much above normal. Much of the western Iberian Peninsula saw 850 hpa winds over 50 kts and +5SD v-wind anomalies as the system approached the coast (FIG. 5b-c). The strong winds then impacted the coastal regions of France (Fig. 5d-e). The +5 to +6SD v-winds are visible over France at 27/1800 and 28/0000 UTC (Figs. 5d-e). The larger anomalies were in eastern France. The strong south-southwest winds along the French Coast between 27/1800 and 28/0000 UTC likely favored forcing wave action into the coastal zone. It is interesting to note that a band of +3SD winds developed in eastern France around 27/1200 UTC well ahead of the main band of strong southerly winds. This may indicate some unique interactions with the larger scale system with complex terrain and the Alps to south of this evolving feature (Fig. 5c-e). The strong 850 hpa jet weakened a bit as it moved north. Northern Germany saw strong winds though the v-wind anomalies were lower over Germany and lower still as they moved over Poland by 01/00000 UTC (Fig. 5i). The 850 hpa u-wind anomalies (Fig. 7) showed strong easterly winds north of the 850 hpa cyclone center. However, the westerly winds south of the 850 hpa low track were significantly stronger and more noteworthy. The strong southwest winds east of Gibraltar at 27/1200 UTC were 4 to 5SDs above normal u-wind anomalies (Fig. 7c). As these strong winds moved over the Mediterranean Basin the 50 to 70kt winds were 5 to 6SDs above normal (Fig. 7e). The westerly winds weakened as this low-level jet approached Sardinia. iii. Ensemble Forecasts The ensemble means and anomalies valid at 27/1800 UTC for the PW, 850 hpa winds and mean sea level pressure fields from 9 forecast cycles are shown in Figures 8-10. The PW data (Fig. 8) shows the surge o high PW air into Western Europe quite similar to that which was observed. The GEFS also predicted the deep cyclone (Fig. 10) and the cyclone track (not shown) and the strong 850 hpa winds (Fig. 9). The wind anomalies were on the order of +5SDs above normal. Using the total winds worked well in this case as the damaging winds were strong southsouthwesterly winds. The GEFS accumulated QPF is shown in Figure 11. These data suggest locally heavy rainfall was possible over the western Iberian Peninsula. Most of the 9 GEFS cycles showed 32 to 64 mm of QPF. Due to the resolution of the model, higher precipitation amounts in the mountains and terrain favored regions was likely under forecast. iv. Impacts and weather As mentioned in the introduction, this storm Caused over 1 million homes to lose power. Caused flooding and had several flood related deaths. Strong surf, high tides, and a storm surge breached a 200 year old sea wall causing the most of the fatalities associated with the storm. Caused major airports to close. Flood tracks and power losses caused trains to be canceled and delayed. 4. CONCLUSIONS A destructive late winter storm pounded the Iberian Peninsula, the French Coastline and other locations of Western Europe from France to Germany. A collapsed sea wall in France was the cause of the majority of fatalities associated with this event. The event was relatively well predicted by the NCEP GEFS and by the European Center for Medium range forecasting ensemble prediction systems. The ECMWF Extreme Forecast Indices (EFI) indicated a high probability for high wind and heavy rainfall 2. Clearly the NCEP EFS 2 Personal Communication Tim Hewson ECMWF.
predicted a strong storm with anomalous winds and the potential for locally heavy rainfall. The data presented here suggest that an anomalous cyclone with deep pressure, strong winds, with significant low-level wind anomalies provided clues and signals for a potential significant event. If the simple anomalies derived from climatology showed such an event it is not surprising that the ECMWF EFI, based on the EFS s built in climatology could detect and predict this storm. The ECMWF high resolution EFS and deterministic model forecasts of the potential 1 km maximum winds exceeding the specified values is shown in Figure 12 3. The area of winds over 50 kts is clearly depicted over the Iberian Peninsula and the Bay of Biscay. A few locations in that general region were forecast to have over 80kts winds. Coincidentally, the East Coast Cyclone along the coast of the United States was predicated to have winds of 30 to 35kts. This product clearly demonstrates the value of ensemble tools to highlight significant weather events. Figure 13 shows the ECMWF EFI for precipitation, winds, and 2m temperatures relative to M-climate. The left side shows that the winds were predicted, days in advance, to be considerably stronger than in the model climatology. The model was clearly predicting a record event relative to its internal climatology. The probabilities on the right side suggest this was a high probability outcome and at shorter ranges the probability was near 100%. Clearly, from an ECMWF ensemble perspective this event was extremely well predicted about 5 days in advance. There are some interesting forecast and philosophical issues one can consider when viewing and interpreting these data. From a traditional anomalies perspective, the data in Figures 5 and 7 suggest the strong winds and tidal flooding along the French Atlantic coast came with strong south-southwest winds. The fact that this pattern and its attendant anomalies were predicted by the GEFS suggests that this storm was relatively well predicted and had a fairly long predictability horizon 5. Acknowledgements Tim Hewson of the ECMWF for information and insights into the storm and forecast and analysis information related to the storm. 6. REFERENCES Doty, B. E., and J. L. Kinter III, 1995: Geophysical data and visualization using GrADS. Visualization Techniques Space and Atmospheric Sciences, E. P. Szuszczewicz and Bredekamp, Eds., NASA, 209 219. Grumm, R.H. and R. Hart. 2001: Standardized Anomalies Applied to Significant Cold Season Weather Events: Preliminary Findings. Wea. and Fore., 16,736 754. Grumm, R.H., and R. Hart, 2001a: Anticipating Heavy Rainfall: Forecast Aspects. Preprints, Symposium on Precipitation Extremes, Albuquerque, NM, Amer. Meteor. Soc., 66-70. Grumm, R.H., and R. Holmes, 2007: Patterns of heavy rainfall in the mid-atlantic. Pre-prints, Conference on Weather Analysis and Forecasting, Park City, UT, Amer. Meteor. Soc., 5A.2. Grumm, Richard H. 2000, "Forecasting the Precipitation Associated with a Mid-Atlantic States Cold Frontal Rainband", NWA Digest, 24, 37-51. Hart, R. E., and R. H. Grumm, 2001: Using normalized climatological anomalies to rank synoptic scale events objectively. Mon. Wea. Rev., 129, 2426 2442. 3 Thanks to Tim Hewson of the ECMWF for the images.
Junker, N.W., R.H. Grumm,R.H. Hart, L.F Bosart, K.M. Bell, and F.J. Pereira, 2008: Use of normalized anomaly fields to anticipate extreme rainfall in the mountains of northern California.Wea. Forecasting, 23,336-356. --------, M.J. Brennan, F. Pereira, M.J. Bodner, and R.H. Grumm, 2009: Assessing the Potential for Rare Precipitation Events with Standardized Anomalies and Ensemble Guidance at the Hydrometeorological Prediction Center. Bull. Amer. Meteor. Soc., 90, 445 453. Neiman, P.J., F.M. Ralph, A.B. White, D.E. Kingsmill, and P.O.G. Persson, 2002: The Statistical Relationship between Upslope Flow and Rainfall in California's Coastal Mountains: Observations during CALJET. Mon. Wea. Rev., 130, 1468 1492.,, G.A. Wick, J.D. Lundquist, and M.D. Dettinger, 2008: Meteorological Characteristics and Overland Precipitation Impacts of Atmospheric Rivers Affecting the West Coast of North America Based on Eight Years of SSM/I Satellite Observations. J. Hydrometeor., 9, 22 47. Stuart, N.A., and R.H. Grumm, 2006: Using Wind Anomalies to Forecast East Coast Winter Storms. Wea. Forecasting, 21, 952 968.
Figure 3. As in Figure 2 except 250 hpa winds and anomalies.
Figure 4. As in Figure 2 except precipitable water (mm) and precipitable water anomalies. Return to text.
Figure 6. As in Figure 1 except for 850 hpa temperatures and temperature anomalies.. Return to text
Figure 5. As in Figure 1 except for 850 hpa winds (kts) and 850 hpa v-wind anomalies.. Return to text
Figure 7. As in Figure 6 except 850 hpa winds and u-wind anomalies.. Return to text
Figure 8. GEFS forecasts of ensemble mean precipitable valid at 1800 UTC 27 February 2010 from forecasts initialized at a) 1200 UTC 24 February, b) 0000 UTC 25 February, c) 1200 UTC 25 February, d) 1800 UTC 25 February, e) 0000 UTC 26 February, f) 0600 UTC 26 February, g) 1200 UTC 26 February, h) 1800 UTC 26 February and i) 0000 UTC 27 February 2010.. Return to text.
Figure 9. As in Figure 8 except for 850 hpa winds and total wind anomalies.. Return to text
Figure 10. As in Figure 8 except for GEFS mean sea level pressures and anomalies.. Return to text
Figure 11. As in Figure 8 except total accumulated precipitation valid for the period ending at 1800 UTC 18 February 2010. Return to text.
Figure 12. ECWMF ensemble and high resolution deterministic model the large colored dots show the maximum 1 km winds (kts) with a 300 mile radius of the dot. The isoabars are from the higher resolution deterministic model run. Arrow focus the text discussion. Blue arrow shows the Iberian Peninsula region and the red arrow shows the East Coast.
Figure 13 ECMWF EFI for a point near the Coast of France. The data show the model climate (black) and the forecast cycles distribution values relative to the model climate. On the left side each run is compared to the model climate on the. These data for the winds show that all the forecast cycles were predicting winds far stronger than the long term 5-member ensemble climate (M-Climate). The wind data also show that the 0 to 24 hour lead time run, 100% of the members predicted winds well above M-climate values. Even at 108-132 hours at least 71% of the members predicted strong winds relative to M-climate. The precipitation field showed trend with higher than M-climate precipitation indicating a significant precipitation event. The shorter range forecasts indicated this trend too, however due to the time range they had sharper cut-off in the QPF.
Figure A1. UKMET office analysis of the storm off the Coast of France with a 967 hpa center valid at 0000 UTC 28 February 2010.