Page 1© Crown copyright 2005 Met Office seasonal predictions and applications Richard Graham Chris Gordon, Matt Huddleston, Mike Davey, Alberto Arribas,

© Crown copyright 2005 Page 1

Met Office seasonal predictions and applicationsRichard 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


Outline

Met Office systems & basic productsEurope/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)


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 (1987-2001 calibration)• run at ECMWF as part of developing European multi-model – EURO-SIP

Ocean Analysis - 5 member ensemble

Real - TimeForecast

41 memberensemble

1987 20051988

Atmosphere NWP/re- analyses

15 member


Example website products for GloSea & EURO-SIP

Latest (May) GloSea ensemble forecast for tropical Pacific (Niño3.4) Sea Surface Temperature (SST)

Products available at: www.metoffice.gov.uk/research/seasonal

P(above)

P(avge)

P(below)

Global JJA temperature probability (tercile categories)

JJA temperature probability – ‘extremes’ (outer-quintile categories)

GloSea EURO-SIP

P(well-below)

P(well-above)


Statistical forecasts for specific regions – based on historical SST anomaly relationships

winter NAO

Used in objective and subjective combination with GloSea model output


winter 2005/6 forecast 2005/6


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.

Observed temperature anomalies DJF 2005/6

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


NAO statistical/empirical forecast, winter 2005/06

NAO index: difference between normalised pressure anomaly Azores - Iceland

N. Atlantic May SST anomaly associated with +ve NAO

N. Atlantic May SST anomaly 2005

Predicts correct sign in 2 out of 3 winters


Met Office decadal prediction system (DePreSys)DJF forecast from June 2005


GloSea & HadAM3 skill and ‘response’

‘average’ DJF hindcast skill1987-2002 (ROC)

courtesy W. Norton

Model skill/’response’

HadAM3 response to idealised (‘May05-like’) forcing


GloSea predictions: Temperature forecast for DJF. Ensemble mean relative to 1987-2001 climatology

OSTIA anomaly 1985-2001 climatology

From September

From November

From October


GloSea: 500 hPa forecast for DJF – Ensemble mean

NCEP Analysis

From September From October

From November

M

DAMM

M

Model ~ 40% observed


Precipitation winter 05/06: ‘…some indication of drier-than-average’

‘average’ DJF hindcast skill1987-2002 (ROC)

GloSea prediction from Sep05

Most-likely precipitation category, DJF05/06

Observed precip anomalies DJF05/06 (IRI)


Meteo-France

ECMWFMet Office (GloSea)

EURO-SIP: probability of lower temperature tercile category: NDJ 2005 (from September)

Forecast is made available on the 15th of each month.

EURO-SIP multi-model


Monitoring the forecast – ocean temperatures

May 2005 October 2005

August 2005Below the surface 60-90m

October 2005


Monitoring the forecast

January 1996

January 2006

Gulf Stream region

Sub-tropical region

Note impact of ARGO array

South of Newfoundland region

0m

100m

50m

May Dec

150m


The forecast process

‘This forecast is produced using a combination of statistical models and complex climate models with interpretation by operational forecasters.’

Dynamicalforecasting models

Analysis ofcurrent oceanobservations

Statisticalforecasting model

Analysis ofclimate trends

Skill assessed by past performance of the forecast methods

Monthly conference of experts (forecasting,

research & comms staff)

(Met Office,EURO-SIP)

Research studies(e.g. PREDICATE,

COAPEC)

What other forecasts

are saying


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.


Accounting for climate trends

&

Communication issues


Some press (over)reactionThe ‘how cold is cold?’ issue

27th October 2005 31st October 2005


Choice of climatology determines the forecast message!Statistical forecast for summer 2006 relative to 3 climatologies

Relative to 1987-2001 (CGCM hindcast period)

‘Most likely cold’

Relative to 1971-2000

‘Most likely average’

Relative to 1961-1990

‘Most likely average’


Winter (DJF) 2005/6 forecast ‘re-stated’:forecast probabilities for Southern England, from Sept

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

-6 -5 -4 -3 -2 -1 0 1 2 3

Temperature anomaly degC

Pro

ba

bili

ty

trend adjusted climatology forecast

1962/63

2002/03

1995/96

2003/042004/05

1984/85

1989/90

(4.72 ºC)

+0.015ºC/year 1975 on,

+0.0075ºC/year before 1975

Climate 1915 to 2005

2005/06

Skill-calibrated combination of predicted NAO index and GloSea 2m temperature


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


Forecasts for Africa Regional Climate Outlook Forums


West Africa Regional Climate Outlook Forum for precipitation JAS 2005

CGCM ‘large-scale’ quality sufficient for downscaling?

ability of downscaling to improve regional skill?

benefits of dynamical Vs statistical methods?

GloSea skill 2m lead GloSea probabilities RCOF forecast

wet

dry

avgeObserved (IRI)

Verification


Predicted, observed 2005 and LTA inflow

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

June - Nov July - Nov Aug - Nov Sept - Nov Oct - Nov

Mill

ion

Ac

re F

ee

t (M

AF

)

2005 UK-Met Inflow (MAF)

2005 Actual Inflow (MAF)

LTA

Operational forecasts for 2005

Applications: water volume inflow, lake Volta:learning to use in decision making

Akosombo dam:1000MWatt Hydro-plant

Limit of catchment

Lake Volta

0

10

20

30

40

50

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

perc

ent o

f ann

ual t

otal

rainfall

inflow

Low inflow forecasts viewed with caution

0

50

100

150

200

250

300

1965 1970 1975 1980 1985 1990 1995 2000 2005

year

infl

ow

an

om

aly

(%

of

no

rmal)

Real-time forecasts

Corr=0.69

June issue forecasts of Jul-Oct inflow

forecast

verificationRegression:GloSea+statistical+catchment observations


GPC forecasts for OND available for GHACOF16, the published consensus, the verification

Observed OND precipitation anomalies

GloSea Euro-SIP ECMWFIRI

Published Consensus (SOND)


Additional slides


Accounting for climate trends in seasonal forecasts:Japan December 2005

•Figure from Koichi Kurihara, JMA


Use of hindcasts: calibration can dilute CGCM ‘signal’ relevant to the current forecast situation

Reliability for outer-quintile temperature categories, northern exttratropics

Resolution

‘ability to detect outer-quintile temperature events’

‘Raw’ GloSea ensemble Calibrated using hindcast performance


Precip: JJA

Skill at 1 month lead: ROC scores based on hindcasts 1987-2002

Upper tercile category Upper quintile category

Temp: MAM


User requirement for regional detail:Example: observed regional impact of negative NAO

Average number of days with mean temperature < 0°C

10 winters with –ve NAO, 1970/1 – 2000/1

9 winters since 1995/96

Based on station observations

more ‘cold’ days in all districts (factor 3 to 8)

increase largest in south and west

When –ve NAO is observed


User requirement for regional detail

Average number of days with mean temperature < 0°C

10 winters with –ve NAO, 1970/1 – 2000/1

9 winters since 1995/96

When –ve NAO is forecast

more ‘cold’ days in all districts (factor 2 to 5)

increase largest in south and west


Inputs: Underpinning scientific understandingFrom Warwick Norton (Reading Uni): HadAM3 forcing experiments

Solid contours are significant at 95%

• Rossby wave train over Atlantic, ridge over northern Europe gives cold temps.


Previous Dec-Jan with strong Atlantic dipole SST pattern (9 years)

Solid contours are significant at 95%

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Page 1© Crown copyright 2005 Met Office seasonal predictions and applications Richard Graham Chris Gordon, Matt Huddleston, Mike Davey, Alberto Arribas,