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

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

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 Monthly Forecast Day Seasonal Forecasts Month 2-7 Seasonal Forecasts Month 2-7 Forecasting systems at ECMWF

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

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

Exeter 1-3 December 2010 The ECMWF monthly forecasting system

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

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

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

Exeter 1-3 December 2010 The Madden Julian Oscillation

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

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

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

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

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

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

Exeter 1-3 December Probabilistic skill scores – NDJFMA Reliability Diagram Probability of 2-m temperature in the upper tercile Day Europe Strong MJO in IC Weak MJO in IC N. Extratropics -0.06

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

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

Exeter 1-3 December 2010 Tropical storm strike probability WEEK 1Week 2Week 3 Weak MJO Strong MJO ROC AREA over SH Day 5-11Day Day Day 26-32

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

Exeter 1-3 December 2010 Soil Moisture Initial Conditions

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

Exeter 1-3 December 2010 Stratospheric initial conditions

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

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

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

Exeter 1-3 December day EPS experiment Comparison with System 3

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

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

Exeter 1-3 December 2010 Interannual variability of June rainfall over India CorrelationRMS ERROR VAREPS- 15 May Seas - Month 2 Seas – Month Verification: 1 o x1 o gridded daily rainfall data from IMD

Exeter 1-3 December 2010 Interannual variability of Atlantic hurricanes AugustSeptemberOctober VAREPS- 15th Seas - Month 1 Seas – Month Correlation with HURDAT

Exeter 1-3 December 2010 Conclusion Forecasts for days that are generally better than climatology and persistence of day 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.

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

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

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

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.

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

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

Exeter 1-3 December 2010 MJO Propagation ForecastAnalysis

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