CPC predictions - Atmospheric and Oceanic Science

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/ 1 May22,2013,/Nov20,2013/April,23,2014/

Assorted Underlying Issues • • • • • • • •

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 2

Menu of CPC predictions: • • • • •

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/9 0day/tools/briefing/index.pri.html 3

EXAMPLE P U B L I C L Y I S S U E D

“ O F F I C I A L ” F O R E C A S T

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From an internal CPC Briefing package

EMP

EMP

EMP

N/A

DYN

EMP

DYN CON

EMP

CON 8

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-T Method: CCA X OCN X CFS X SMLR X ECCA X Consolidation X

US-P X X X X X X

SST

US-soil moisture

X X

X

X

Constr Analog X X X X Markov X ENSO Composite X X Other (GCM) models (IRI, ECHAM, NCAR,  N(I)MME): X X CCA = Canonical Correlation Analysis OCN = Optimal Climate Normals CFS = Climate Forecast System (Coupled Ocean-Atmosphere Model) SMLR = Stepwise Multiple Linear Regression CON = Consolidation 10

Long Lead Predictions of US Surface Temperature using Canonical Correlation Analysis. Barnston(J.Climate, 1994, 1513) Predictor - Predictand Configuration Predictors

Predictand

* Near-global SSTA * N.H. 700mb Z

* US sfc T

* US sfc T four predictor “stacked” fields 4X652=2608 predictors

one predictand period

102 locations

Data Period 1955 - last month

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About OCN. Two contrasting views: - Climate = average weather in the past - Climate is the ‘expectation’ of the future 30 year WMO normals: 1961-1990; 1971-2000; 1981-2010 etc OCN = 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-normal plus 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 better 3) somewhat shorter averages are better (for T) 14 see Huang et al 1996. J.Climate. 9, 809-817.

OCN has become the bearer of most of the skill, see also EOCN method (Peng et al), or other alternatives of projecting normals forward.

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G H C N C A M S F A N 2 0 0 8

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Preview of 2010s, 4 years only

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NCEP’s Climate Forecast System, now called CFS v2 • 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 2014.19

NCEP’s Climate Forecast System, now called CFS v2