How Does NCEP/CPC Make Operational Monthly and Seasonal Forecasts?. 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/. Assorted Underlying Issues. Which tools are used…
Huug van den Dool (CPC)
CPC, June 23, 2011/ Oct 2011/ Feb 15, 2012
/ UoMDMay,2,2012/ Aug2012/ Dec,12,2012/UoMDApril24,2013/
6-10 day (daily)
Week 2 (daily)
Monthly (monthly + update)
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)
From an internal CPC Briefing package
(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
Out of date diagram.
‘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’?
SEC and CV
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)
2012 or 2013
t=1956 or 1957
2012 or 2013
t=1956 or 1957
Where X is any variable (soil moisture, temperature, precipitation)
Source: Wanqiu Wang
Two meetings to Discuss the Seasonal Forecast.