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Met Office seasonal predictions and applications

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1 Met Office seasonal predictions and applications
Richard Graham Chris Gordon, Matt Huddleston, Mike Davey, Alberto Arribas, Bernd Becker, Anca Brookshaw, Andrew Colman, Stephen Cusack, Margaret Gordon, Bruce Ingleby, Peter McLean (Adam Scaife, Malcolm Macvean) ECWMF Forecast Users Meeting, 16 June 2006 © Crown copyright 2005

2 Outline Met Office systems & basic products
Europe/UK winter 2005/06 (first major operational UK seasonal forecast statement) Accounting for climate trends in forecasts and their communication If time: forecasts for Regional Climate Outlook Forums (RCOFs) © Crown copyright 2005

3 Ocean Analysis - 5 member ensemble
Global prediction: Dynamical Seasonal forecasting system : GloSea Enhanced version of the Hadley Centre Climate model HadCM3 AGCM: 2.5° x 3.75° x 19L OGCM: (1.25° to 0.3°) x 1.25° x 40L 41-member ocean-atmosphere global forecast ensemble run to 6 months ahead from initial conditions on 1st of each month 5 ocean analyses from perturbed wind stresses Ocean analyses further perturbed with instantaneous SST perturbations hindcast (‘BACKRUN’) period, 1987-present ( calibration) run at ECMWF as part of developing European multi-model – EURO-SIP Atmosphere NWP/re- analyses Real - Time Forecast 41 member ensemble 15 member Ocean Analysis - 5 member ensemble 1987 © Crown copyright 2005 1988 2005

4 Example website products for GloSea & EURO-SIP
P(above) P(avge) P(below) Global JJA temperature probability (tercile categories) Latest (May) GloSea ensemble forecast for tropical Pacific (Niño3.4) Sea Surface Temperature (SST) JJA temperature probability – ‘extremes’ (outer-quintile categories) GloSea EURO-SIP P(well-below) P(well-above) Products available at: © Crown copyright 2005

5 Statistical forecasts for specific regions – based on historical SST anomaly relationships
winter NAO Used in objective and subjective combination with GloSea model output © Crown copyright 2005

6 winter 2005/6 forecast 2005/6 © Crown copyright 2005

7 Met Office winter forecast 2005/6
A two in three chance of a colder-than-average winter for much of Europe. If this holds true, parts of the UK – especially southern regions – are expected to have temperatures below normal There is also an indication for a drier-than-average winter over much of the UK. Customers: public government (Cabinet office) planners in utilities, transport, finance & insurance, defence, aviation, local authorities biggest ‘story’ ever run by Met Office press office 71% of public aware, 14% took action Observed temperature anomalies DJF 2005/6 © Crown copyright 2005

8 NAO statistical/empirical forecast, winter 2005/06
N. Atlantic May SST anomaly associated with +ve NAO NAO index: difference between normalised pressure anomaly Azores - Iceland Predicts correct sign in 2 out of 3 winters N. Atlantic May SST anomaly 2005 © Crown copyright 2005

9 Met Office decadal prediction system (DePreSys) DJF forecast from June 2005
© Crown copyright 2005

10 GloSea & HadAM3 skill and ‘response’
‘average’ DJF hindcast skill (ROC) courtesy W. Norton Model skill/’response’ HadAM3 response to idealised (‘May05-like’) forcing © Crown copyright 2005

11 GloSea predictions: Temperature forecast for DJF
GloSea predictions: Temperature forecast for DJF. Ensemble mean relative to climatology From September From October From November OSTIA anomaly climatology © Crown copyright 2005

12 GloSea: 500 hPa forecast for DJF – Ensemble mean
From September From October M M From November Model ~ 40% observed NCEP Analysis M DAM © Crown copyright 2005

13 Precipitation winter 05/06: ‘…some indication of drier-than-average’
GloSea prediction from Sep05 ‘average’ DJF hindcast skill (ROC) Most-likely precipitation category, DJF05/06 Observed precip anomalies DJF05/06 (IRI) © Crown copyright 2005

14 EURO-SIP: probability of lower temperature tercile category: NDJ 2005 (from September)
Met Office (GloSea) ECMWF EURO-SIP multi-model Meteo-France Example of large differences between the models predictions. Europe Eastern Atlantic and Canada Forecast is made available on the 15th of each month. © Crown copyright 2005

15 Monitoring the forecast – ocean temperatures
May 2005 October 2005 Below the surface 60-90m October 2005 August 2005 © Crown copyright 2005

16 Monitoring the forecast
Gulf Stream region January 1996 50m 100m 150m May Dec January 2006 South of Newfoundland region Sub-tropical region Note impact of ARGO array © Crown copyright 2005

17 Monthly conference of experts (forecasting, research & comms staff)
The forecast process ‘This forecast is produced using a combination of statistical models and complex climate models with interpretation by operational forecasters.’ Statistical forecasting model Research studies (e.g. PREDICATE, COAPEC) Dynamical forecasting models (Met Office,EURO-SIP) Monthly conference of experts (forecasting, research & comms staff) What other forecasts are saying Skill assessed by past performance of the forecast methods Analysis of current ocean observations Analysis of climate trends © Crown copyright 2005

18 Summary The statistical forecast suggested colder than average winter (it was supported by the experimental decadal forecast system). GloSea September and October forecasts suggested cold conditions over Europe. GloSea forecast the SST tripole and geopotential height patterns consistent with a negative NAO situation – but the signal is weak ~ 40% of observed amplitude (as expected). Real time analysis of sub-surface ocean temperatures supported the re-emergence of tripole SST anomalies in winter. This was closely (weekly) monitored to see if the forecast was ‘on track’. Expert interpretation (by research and forecast staff) was used to draw all this together into the headline forecast and to subsequently decide if the forecast should be revised. © Crown copyright 2005

19 Accounting for climate trends
& Communication issues © Crown copyright 2005

20 Some press (over)reaction The ‘how cold is cold?’ issue
31st October 2005 27th October 2005 © Crown copyright 2005

21 Choice of climatology determines the forecast message
Choice of climatology determines the forecast message! Statistical forecast for summer 2006 relative to 3 climatologies Relative to (CGCM hindcast period) ‘Most likely cold’ Relative to ‘Most likely average’ Relative to ‘Most likely average’ © Crown copyright 2005

22 Winter (DJF) 2005/6 forecast ‘re-stated’: forecast probabilities for Southern England, from Sept
Skill-calibrated combination of predicted NAO index and GloSea 2m temperature 2002/03 2003/04 2004/05 1995/96 2005/06 1989/90 1984/85 1962/63 (4.72 ºC) +0.015ºC/year 1975 on, ºC/year before 1975 Climate 1915 to 2005 © Crown copyright 2005

23 Concluding remarks Advice was favourably received by UK government – raised profile of SF Met Office now contracted for routine ‘operational’ seasonal forecast briefings to Cabinet Office …and to Environment Agency re drought in SE UK. transfer of ‘operational’ tasks from Research to Operations Centre Need ‘pull-through’ of existing understanding to improve CGCMs new post focused on improving European skill, also NERC knowledge transfer post ENSEMBLES project comparison of decadal and seasonal models Improve communication being developed for next winter ‘how cold is cold?’ based on feedback (in part from April RMS meeting) issue more detailed probability information avoid confusion caused by displaying component forecasts on the website (NAO and GloSea output) ‘consolidated’ forecast maps (combining forecasts) Hindcasts do not give full skill picture – need to know how the models perform under different modes of forcing this impacts on model calibration/combining strategies Need ways of accounting for climate trend in the preparation and communication of the forecast © Crown copyright 2005

24 Forecasts for Africa Regional Climate Outlook Forums
© Crown copyright 2005

25 West Africa Regional Climate Outlook Forum for precipitation JAS 2005
GloSea skill 2m lead GloSea probabilities RCOF forecast wet Observed (IRI) Verification avge CGCM ‘large-scale’ quality sufficient for downscaling? ability of downscaling to improve regional skill? benefits of dynamical Vs statistical methods? dry © Crown copyright 2005

26 Applications: water volume inflow, lake Volta: learning to use in decision making
Real-time forecasts Corr=0.69 June issue forecasts of Jul-Oct inflow forecast verification Regression:GloSea+statistical+catchment observations Limit of catchment Lake Volta Akosombo dam: 1000MWatt Hydro-plant Operational forecasts for 2005 Low inflow forecasts viewed with caution © Crown copyright 2005

27 GPC forecasts for OND available for GHACOF16, the published consensus, the verification
IRI GloSea ECMWF Euro-SIP Observed OND precipitation anomalies Published Consensus (SOND) © Crown copyright 2005

28 Additional slides © Crown copyright 2005

29 Accounting for climate trends in seasonal forecasts: Japan December 2005
Figure from Koichi Kurihara, JMA © Crown copyright 2005

30 Use of hindcasts: calibration can dilute CGCM ‘signal’ relevant to the current forecast situation
‘Raw’ GloSea ensemble Calibrated using hindcast performance Reliability for outer-quintile temperature categories, northern exttratropics Resolution ‘ability to detect outer-quintile temperature events’ © Crown copyright 2005

31 Skill at 1 month lead: ROC scores based on hindcasts 1987-2002
Upper tercile category Upper quintile category Temp: MAM Precip: JJA © Crown copyright 2005

32 User requirement for regional detail: Example: observed regional impact of negative NAO
Average number of days with mean temperature < 0°C When –ve NAO is observed 10 winters with –ve NAO, 1970/1 – 2000/1 9 winters since 1995/96 more ‘cold’ days in all districts (factor 3 to 8) increase largest in south and west Based on station observations © Crown copyright 2005

33 User requirement for regional detail
Average number of days with mean temperature < 0°C When –ve NAO is forecast 10 winters with –ve NAO, 1970/1 – 2000/1 9 winters since 1995/96 more ‘cold’ days in all districts (factor 2 to 5) increase largest in south and west © Crown copyright 2005

34 Inputs: Underpinning scientific understanding
From Warwick Norton (Reading Uni): HadAM3 forcing experiments Solid contours are significant at 95% Precip anomaly over Carribean, and northward shift in the ITCZ in Atlantic and East Pacific. Enhanced moisture and temperatures driven by trades. Wave train extending over N. America, North Atlantic and Europe. Ridging over N. Atlantic brings cold air down over Eastern Europe - anomalies -1.5C Rossby wave train over Atlantic, ridge over northern Europe gives cold temps. © Crown copyright 2005

35 Previous Dec-Jan with strong Atlantic dipole SST pattern (9 years)
Solid contours are significant at 95% © Crown copyright 2005

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