1. An unusual Saharan dust outbreak into central Europe and heavy precipitation at the southern side of the Alps in May 2008: A TIGGE case study Lars Wiegand 1,2, Arwen Twitchett 2, Conny Schwierz 3 & Peter Knippertz 2 Third THORPEX International Science Symposium, Monterey: 14-18 Sept. 2009 123

2. Third THORPEX International Science Symposium, Monterey: 14-18 September 2009 MotivationUpper-Level DevelopmentHigh Impact Weather Conclusion Outline  Motivation  Upper-Level Development  RMSE/SPREAD  analysis errors  position of forecasted streamers  High Impact Weather  Saharan dust storm  heavy precipitation in Southern Switzerland  Conclusions

3. Third THORPEX International Science Symposium, Monterey: 14-18 September 2009 MotivationUpper-Level DevelopmentHigh Impact Weather Conclusion Motivation 2008/05/27 10UTC2008/05/27 13UTC article in newspaper „Süddeutsche“ 2008/05/29: „Die Sahara über Deutschland“ Gornergletscher 08/2008, dust from 05/2008 albedo increase  ablation increase  mass balance decrease Motivation

4. Third THORPEX International Science Symposium, Monterey: 14-18 September 2009 MotivationUpper-Level DevelopmentHigh Impact Weather Conclusion Motivation  widespread heavy precipitation caused:  flooding on the Alpine south side of Switzerland and Italy  Lake Maggiore rised by 10 cm in just 24 hours Motivation 4-day sum of precipitation (26th – 29th of May 2008) mm data: ENSEMBLE (gridded data set from rain gauges)

5. Third THORPEX International Science Symposium, Monterey: 14-18 September 2009 MotivationUpper-Level DevelopmentHigh Impact Weather Conclusion Analysis End of May 2008 (21 st -26 th ) Upper-Level Development upper level PV operational analysis ECMWF region of interest (29-55N, 15W-2E)

6. Third THORPEX International Science Symposium, Monterey: 14-18 September 2009 MotivationUpper-Level DevelopmentHigh Impact Weather Conclusion RMSE of all models (Box: 29-55N, 15W-2E) ECMWF_europe BoM_australia CMA_china CMC_canada CPTEC_brazil JMA_japan KMA_korea NCEP_usa UKMO_uk RMSE calculated with Analysis from ECMWF RMSE calculated with every Centers own Analysis Upper-Level Development

7. Third THORPEX International Science Symposium, Monterey: 14-18 September 2009 MotivationUpper-Level DevelopmentHigh Impact Weather Conclusion 0,22 (USA, Interpolation) 0,44 (Korea, 3Dvar) 0,59 (China, Interpolation) 0,23 (Brazil, USA Interpolation) 0,26 (Japan, 4Dvar) 0,41 (Australia, Interpolation) 0,23 (UK, 4Dvar) 0,25 (Canada, 4Dvar) RMSE in box -0.51.01.5-1.50.5 Upper-Level Development (4Dvar)

8. Third THORPEX International Science Symposium, Monterey: 14-18 September 2009 MotivationUpper-Level DevelopmentHigh Impact Weather Conclusion “non-dispersive” CMA_china CMC_canada ECMWF_europe JMA_japan RMSE & SPREAD RMSE SPREAD (slightly) overdispersiveunderdispersive BoM_australia CPTEC_brazil NCEP_usa UKMO_uk KMA_korea Upper-Level Development

9. Third THORPEX International Science Symposium, Monterey: 14-18 September 2009 MotivationUpper-Level DevelopmentHigh Impact Weather Conclusion Position of Streamer (center of mass) Upper-Level Development 48h forecast position of ECMWF analysis envelope of member positions ECMWF_europe BoM_australia CMA_china CMC_canada CPTEC_brazil JMA_japan KMA_korea NCEP_usa UKMO_uk 96h forecast 120h forecast 168h forecast

10. Third THORPEX International Science Symposium, Monterey: 14-18 September 2009 MotivationUpper-Level DevelopmentHigh Impact Weather Conclusion Saharan dust outbreak  RGB composite: purple color = dust  from 2008/05/26: 09UTC – 23UTC  needed for dust mobilization: u 925hPa > 10 m/s High Impact Weather

11. Third THORPEX International Science Symposium, Monterey: 14-18 September 2009 MotivationUpper-Level DevelopmentHigh Impact Weather Conclusion Region of interest (5W-10E & 23N-35N) number of grid points in box: 208 number of gp, wind > 10m/s: 113 High Impact Weather

12. Third THORPEX International Science Symposium, Monterey: 14-18 September 2009 MotivationUpper-Level DevelopmentHigh Impact Weather Conclusion Grid points where wind > 10m/s ECMWF_europe BoM_australia CMA_china CMC_canada CPTEC_brazil JMA_japan KMA_korea NCEP_usa UKMO_uk High Impact Weather median of centres forecasts ECMWF analysis

13. Third THORPEX International Science Symposium, Monterey: 14-18 September 2009 MotivationUpper-Level DevelopmentHigh Impact Weather Conclusion Precipitation forecast (box average) High Impact Weather ECMWF_europe BoM_australia CMA_china CMC_canada CPTEC_brazil JMA_japan KMA_korea NCEP_usa UKMO_uk median of centres forecasts observed precipitation (ENSEMBLE data set)

14. Third THORPEX International Science Symposium, Monterey: 14-18 September 2009 MotivationUpper-Level DevelopmentHigh Impact Weather Conclusion Conclusions  Open question: which analysis is the “best” one to use?  RMSE smaller with own analysis  Upper-level development  increase of RMSE with lead time  SPREAD of similar magnitude as RMSE in 4 models, 4 models are underdispersive and 1 model is slightly overdispersive  forecasted positions of streamers are mostly too far north  Wind for dust mobilization over Sahara  winds systematically too weak  Precipitation at southern side of Alps  systematically too high in medium-range  mostly too low in short-range Conclusion