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How Does NCEP/CPC Make Operational Monthly and Seasonal Forecasts?

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Huug van den Dool (CPC)

CPC, June 23, 2011/ Oct 2011/ Feb 15, 2012

/ UoMDMay,2,2012/ Aug2012/ Dec,12,2012/UoMDApril24,2013/

May22,2013,/Nov20,2013/April,23,2014/

- Which tools are used…
- How do these tools work?
- How are tools combined???
- Dynamical vs Empirical Tools
- Skill of tools and OFFICIAL
- How easily can a new tool be included?
- US, yes, but occasional global perspective
- Physical attributions

6-10 day (daily)

Week 2 (daily)

Monthly (monthly + update)

Seasonal (monthly)

Other (hazards, drought monitor, drought outlook, MJO, UV-index, degree days, POE, SST) (some are ‘briefings’)

Operational forecasts (‘OFFICIAL’) and informal forecast tools (too many to list)

http://www.cpc.ncep.noaa.gov/products/predictions/90day/tools/briefing/index.pri.html

P

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O

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I

C

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From an internal CPC Briefing package

EMP

EMP

EMP

EMP

N/A

DYN

CON

CON

EMP

DYN

SMLR

CCA

OCN

LAN

OLD-OTLK

CFSV1

LFQ

ECP

IRI

ECA

CON

9

(15 CASES: 1950, 54, 55, 56, 64, 68, 71, 74, 75, 76, 85, 89, 99, 00, 08)

Element US-TUS-P SSTUS-soil moistureMethod:CCA X X XOCN X X CFS X X XXSMLR X XECCA X XConsolidation X X X Constr Analog X X X XMarkov XENSO Composite X XOther (GCM) models (IRI, ECHAM, NCAR, N(I)MME): X XCCA = Canonical Correlation AnalysisOCN = Optimal Climate NormalsCFS = Climate Forecast System (Coupled Ocean-Atmosphere Model)SMLR = Stepwise Multiple Linear RegressionCON = Consolidation

About OCN. Two contrasting views:- Climate = average weather in the past- Climate is the ‘expectation’ of the future30 year WMO normals: 1961-1990; 1971-2000; 1981-2010 etcOCN = Optimal Climate Normals: Last K year average. All seasons/locations pooled: K=10 is optimal (for US T).Forecast for Jan 2015 (K=10) = (Jan05+Jan06+... Jan14)/10. – WMO-normalplus a skill evaluation for some 50+ years.Why does OCN work?1) climate is not constant (K would be infinity for constant climate)2) recent averages are better3) somewhat shorter averages are better (for T)see Huang et al 1996. J.Climate. 9, 809-817.

Preview of 2010s, 4 years only

- MRFb9x, CMP12/14, 1995 onward (Leetmaa, Ji etc). Tropical Pacific only.
- SFM 2000 onward (Kanamitsu et al
- CFSv1, Aug 2004, Saha et al 2006. Almost global ocean
- CFSR, Saha et al 2010
- CFSv2, March 2011. Global ocean, interactive sea-ice, increases in CO2. Saha et al 2014.

<--

Out of date diagram.

Still instructive

‘a-priori’ verification (used to be rare)

After the fact (fairly normal and traditional)

After the fact…..

Source Peitao Peng

(Seasonal) Forecasts are useless unless accompanied by a reliable a-priori skill estimate.Solution: develop a 50+ year track record for each tool. 1950-present.(Admittedly we need 5000 years)

--------- OUT TO 1.5 YEARS -------

OFFicial Forecast(element, lead, location, initial month) = a * A + b * B + c * C +…Honest hindcast required 1950-present. Covariance (A,B), (A,C), (B,C), and(A, obs), (B, obs), (C, obs) allows solution for a, b, c (element, lead, location, initial month)

CFS v1 skill 1982-2003

Fig.7.6: The skill (ACX100) of forecasting NINO34 SST by the CA method for the period 1956-2005. The plot has the target season in the horizontal and the lead in the vertical. Example: NINO34 in rolling seasons 2 and 3 (JFM and FMA) are predicted slightly better than 0.7 at lead 8 months. An 8 month lead JFM forecast is made at the end of April of the previous year. A 1-2-1 smoothing was applied in the vertical to reduce noise.

CA skill 1956-2005

M. Peña Mendez and H. van den Dool, 2008:

Consolidation of Multi-Method Forecasts at CPC.

J. Climate, 21, 6521–6538.

Unger, D., H. van den Dool, E. O’Lenic and D. Collins, 2009: Ensemble Regression.

Monthly Weather Review, 137, 2365-2379.

(1) CTB, (2) why do we need ‘consolidation’?

(Delsole 2007)

SEC

SEC and CV

3CVRE

See also:

O’Lenic, E.A., D.A. Unger, M.S. Halpert, and K.S. Pelman, 2008: Developments in Operational Long-Range Prediction at CPC.Wea. Forecasting, 23, 496–515.

Empirical tools can be comprehensive! (Thanks to reanalysis, among other things). And very economical.Constructed Analogue(next 2 slides)

- Given an Initial Condition, SSTIC (s, t0) at time t0 . We express SSTIC (s, t0) as a linear combination of all fields in the historical library, i.e.
2012 or 2013

- SSTIC (s, t0) ~= SSTCA(s) = Σ α(t) SST(s,t) (1)
t=1956 or 1957

(CA=constructed Analogue)

- The determination of the weights α(t) is non-trivial, but except for some pathological cases, a set of (57) weights α(t) can always be found so as to satisfy the left hand side of (1), for any SSTIC , to within a tolerance ε.

- Equation (1) is purely diagnostic. We now submit that given the initial condition we can make a forecast with some skill by
2012 or 2013

- XF (s, t0+Δt) = Σ α(t) X(s, t +Δt) (2)
t=1956 or 1957

Where X is any variable (soil moisture, temperature, precipitation)

- The calculation for (2) is trivial, the underlying assumptions are not. We ‘persist’ the weights α(t) resulting from (1) and linearly combine the X(s,t+Δt) so as to arrive at a forecast to which XIC (s, t0) will evolve over Δt.

CA-weights in

March 2014

Z500

SST

CA

T2m

Precip

SST

Z500

CFS

T2m

Precip

Source: Wanqiu Wang

- Global SST, mainly ENSO. Tele-connections needed.
- Trends, mainly (??) global change
- Distribution of soil moisture anomalies

- http://origin.cpc.ncep.noaa.gov/products/NMME/

- Friday 2pm June 14
- Tuesday 1:30pm June 18
Two meetings to Discuss the Seasonal Forecast.