1. Exeter 1-3 December 2010 Monthly Forecasting with Ensembles Frédéric Vitart European Centre for Medium-Range Weather Forecasts

2. Exeter 1-3 December 2010 Index The ECMWF monthly forecasting system  Description  Skill Some sources of predictability in the subseasonal time-scale  Madden Julian Oscillation  Stratospheric Sudden Warming  Soil moisture Extension to 46-day – Comparison with seasonal forecasts

3. Exeter 1-3 December 2010 Product ECMWF: Weather and Climate Dynamical Forecasts ECMWF: Weather and Climate Dynamical Forecasts Medium-Range Forecasts Day 1-10(15) Medium-Range Forecasts Day 1-10(15) Monthly Forecast Day 10-32 Monthly Forecast Day 10-32 Seasonal Forecasts Month 2-7 Seasonal Forecasts Month 2-7 Forecasting systems at ECMWF

4. Exeter 1-3 December 2010 Ocean only integration Coupled forecast at TL319 Day 32 EPS Integration at T639 Initial condition Heat flux, Wind stress, P-E Current system (once a week, 51 ensemble members): The ECMWF VarEPS-monthly forecasting system Day 10

5. Exeter 1-3 December 2010 The ECMWF monthly forecasting system Background statistics:  5-member ensemble integrated at the same day and same month as the real-time time forecast over the past 18 years (a total of 90 member ensemble)  Initial conditions: ERA Interim  It runs once every week

6. Exeter 1-3 December 2010 The ECMWF monthly forecasting system

7. Exeter 1-3 December 2010 7 Problem with hindcast initial conditions Probability of T 2m to be in lowest tercile 100 % 0 Forecast of week 1 Start: 11-05-2006 Snow ANALYSIS 11 MAY Observations

8. Exeter 1-3 December 2010 Skill of the ECMWF Monthly Forecasting System ROC score: 2-meter temperature in the upper tercile Day 19-25 Day 26-32 Day 5-11Day 12-18

9. Exeter 1-3 December 2010 9 Monthly Forecast: Performance over the Northern Extratropics Forecast Day 12-18 Persistence of Day 5-11 Forecast Day 19-32 Persistence of Day 5-18 ROC score: 2-meter temperature in the upper tercile Day 12-18Day 19-32

10. Exeter 1-3 December 2010 The Madden Julian Oscillation

11. Exeter 1-3 December 2010 OLR anomalies - Forecast range: day 15 32R3 ERA40 days 29/12 05/01 12/01 20/01 28/01 04/04 12/02 28R329R131R132R2 10/04 04/0509/0606/07 11/07 33R135R135R3 06/08 09/08 09/09

12. Exeter 1-3 December 2010 Experimental setup: -46 day hindcasts at T399/T255. Coupled after day 10. -15 members -Starting dates: 1 st of each month 1989-2008 -Model Cycle 32R3 (operational cycle from 11/07 to 06/08) Hindcast Experiment

13. Exeter 1-3 December 2010 “Perfect Model” Ensemble mean/ reanalysis MJO Skill scores Bivariate Correlation Bivariate RMS error Ensemble Spread Ensemble mean/ reanalysis Climatology

14. Exeter 1-3 December 2010 Impact on the Extratropics- Z500 anomalies

15. Exeter 1-3 December 2010 ERA Interim 32R3 36R1 36R1_relax Impact on the Extratropics- Z500 anomalies

16. Exeter 1-3 December 2010 Phase3+10 days Impact on weather regimes NAO- NAO+ Atlantic ridge Scandinavian blocking Phase6+10 days

17. Exeter 1-3 December 2010 0.04 Probabilistic skill scores – NDJFMA 1989-2008 Reliability Diagram Probability of 2-m temperature in the upper tercile Day 19-25 Europe 0.03 -0.09 Strong MJO in IC Weak MJO in IC N. Extratropics -0.06

18. Exeter 1-3 December 2010 Impact of the MJO on Brier Skill Scores NDJFMA 1989-2008- N. Extratropics DAY 5-11 Z500T850Precip DAY 12-18 Z500T850Precip DAY 19-25DAY 26-32 Z500T850PrecipZ500T850Precip Weak MJO in IC Strong MJO in IC

19. Exeter 1-3 December 2010 MJO Composite- NDJFMA Tropical storm density anomaly Vitart, 2009, GRL

20. Exeter 1-3 December 2010 Tropical storm strike probability WEEK 1Week 2Week 3 Weak MJO0.780.720.68 Strong MJO0.870.790.74 ROC AREA over SH Day 5-11Day 12-18 Day 19-25 Day 26-32

21. Exeter 1-3 December 2010 Impact of ocean-atmosphere coupling Woolnough et al, QJRMS, 2007 Per. SST anomalies ML OGCM

22. Exeter 1-3 December 2010 Soil Moisture Initial Conditions

23. Exeter 1-3 December 2010 23 GLACE2 Series 1 – Series 2 – ECMWF AMIP DAY 0-15 DAY 16-30DAY 31-45 Courtesy Bart van den Hurk

24. Exeter 1-3 December 2010 Stratospheric initial conditions

25. Exeter 1-3 December 2010 Stratospheric Sudden Warmings Impact of vertical resolution. Spread L91 RMS error L91 RMS error L62 Spread L62 Forecast starting on 5/1/06 Forecast starting on 19/1/06 L91L62

26. Exeter 1-3 December 2010 Impact of Better stratospheric vertical resolution Day 12-18Day 19-25Day 26-32 62 levels91 levels Probability that Z500 anomalies are in upper tercile 1 st Feb/May/Aug/Oct 1989-2008 (80 cases)

27. Exeter 1-3 December 2010 Stratospheric Sudden Warmings Impact of S-Svs Forecast 5/01/06 Forecast 26/01/06 Ensemble spread Control S-Svs Work with J. Barkmeijer, T. Jung and M. Leutbecher

28. Exeter 1-3 December 2010 46-day EPS experiment Comparison with System 3

29. Exeter 1-3 December 2010 Global Scores 2MTM- Ensemble mean correlation with analysis August 1981-2007 SEAS- Month 2VEPS

30. Exeter 1-3 December 2010 EPS Day 16-45 46-day EPS extension – DJFM – N. extra. ROC DiagramReliability Diagram Seas Month 2

31. Exeter 1-3 December 2010 Interannual variability of June rainfall over India 1989-2007 CorrelationRMS ERROR VAREPS- 15 May Seas - Month 2 Seas – Month 1 0.62 0.40 0.52 0.90 1.15 0.96 Verification: 1 o x1 o gridded daily rainfall data from IMD

32. Exeter 1-3 December 2010 Interannual variability of Atlantic hurricanes 1981-2007 AugustSeptemberOctober VAREPS- 15th Seas - Month 1 Seas – Month 2 0.77 0.31 -0.03 0.37 0.33 0.23 0.69 0.18 Correlation with HURDAT

33. Exeter 1-3 December 2010 Conclusion Forecasts for days 12-18 that are generally better than climatology and persistence of day 5-11. Beyond 20 days the monthly forecast is marginally skilful. The MJO is the main source of predictability in the northern Extratropics for weeks 3 and 4. Extending EPS forecasts can help to produce more frequent and skilful short-range seasonal forecasts, particularly for some extreme events.

34. Exeter 1-3 December 2010 Future Plans Run the monthly forecasts twice a week Ocean/atmosphere Coupling from day 0 Extend forecast range to 46-60 days

35. Exeter 1-3 December 2010 Multi-model combination ECMWFNCEP (MRF) ECMWF+NCEP Extreme tercile probability forecast. Northern Hemisphere. DJF. 84 cases (1990-2002) T850 Whitaker et al, 2005

36. Exeter 1-3 December 2010 a) Analysis b) Operational MOFC c) MOFC CY31R2d) VAREPS CY31R2 Forecasts started on 23 July 2003 for 2mT anomalies for 3-9 August 2003 (fc day 12-18): impact of model cycle and upgrade to 32-day VAREPS. Test case : Summer 2003 Heat Wave

37. Exeter 1-3 December 2010 The ECMWF VarEPS-monthly forecasting system A 51-member ensemble is integrated for 32 days every week Atmospheric component: IFS with the latest operational cycle and with a T639L62 resolution till day 10 and T319L62 after day 10. Persisted SST anomalies till day 10 and ocean-atmosphere coupling from day 10 till day 32. Oceanic component: HOPE (from Max Plank Institute) with a zonal resolution of 1.4 degrees and 29 vertical levels Coupling: OASIS (CERFACS). Coupling every 3 hours.

38. Exeter 1-3 December 2010 Stratospheric Sudden warming- January 2009 8/1/2009 15/1/2009 SSW Index (T50 gradient)

39. Exeter 1-3 December 2010 Stratospheric Sudden warming- January 2009 15/1/2009 2mtm anomaly Forecast Analysis Composite Good SW Composite Bad SW Day 19-25 Day 26-32

40. Exeter 1-3 December 2010 MJO Propagation ForecastAnalysis

41. Exeter 1-3 December 2010 Convection changes to operational massflux scheme (CY32R3) New formulation of convective entrainment: Previously linked to moisture convergence – Now more dependent on the relative dryness of the environment New formulation of relaxation timescale used in massflux closure: Previously only varied with horizontal resolution – Now a variable that is dependent on the convective turnover timescale i.e. variable in both space and time also Impact of these changes is large including a major increase in tropical variability Bechtold et al, QJRMS, 2008