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Seasonal Forecasts Based on a Statistical Model

In November 1996, Environment Canada began to produce surface air temperature and precipitation anomaly outlooks up to 3 to 9 months ahead using a statistical model called CCA or Canonical Correlation Analysis (Shabbar, 2000; Barnston and Shabbar, 1996; Shabbar, 1996a and Shabbar, 1996b) . This statistical technique was developed by Environment Canada's Climate Monitoring and Data Interpretation division to produces seasonal forecasts of surface air temperature and precipitation anomalies over Canada. The forecast are made at Canadian stations locations up to nine months in advance.

The analysed field of sea surface temperature (SST) anomalies over the previous twelve months provides the forcing. The SST anomalies are obtained from the Meteorological Service of Canada global analysis of mean monthly SST, for each of the 12 months preceding the date on which the forecast is issued. Data from ships, buoys and satellites are assimilated to produce these analyses. The SST anomalies are averaged spatially over 10 X 10 degree grid cells and over three-month periods. The statistical relationships between the observed SST anomalies and the subsequent observed temperature and precipitation anomalies were developed from a 35-year dataset (see details in Shabbar and Barnston, 1996). The climatology of the technique and its skill are derived from this dataset. The climatology of the model is used to calculate the forecast anomaly and its interannual standard deviation to transform to retrieve the predicted categories.

Equations are available to generate forecasts for lead times of up to nine months. Currently, however, only the forecasts for lead times of 3, 6 and 9 months are generated with the CCA method (Servranckx et al. 2000) (Requires Acrobat Reader to view); for the zero lead time, see the forecasts made with the numerical prediction models. The CCA forecasts are available at 51 selected Canadian stations for temperature, and 69 stations for precipitation. The stations were choose to cover as uniformly as possible the Canadian area.

References

Servranckx, R., N. Gagnon, L. Lefaivre and A. Plante, 2000: Environment Canada Seasonal Forecasts: Products, Methods, Procedures and Verification. In the "Proceedings of the sixth workshop on operational meteorology", Halifax, November 1999, 172-176. (Requires Acrobat Reader to view)

Shabbar, A., 1996a: Seasonal prediction of Canadian surface temperature and precipitation by canonical correlation analysis. Proceedings of the 20th Annual Climate diagnostics Workshop, Seattle, Washington, October 23-27, 1995, 421-424.

Shabbar, A., 1996b: Seasonal forecast of Canadian surface temperature by canonical correlation analysis. Preprints of the 13th Conference on Probability and Statistics in the Atmospheric Sciences, San Francisco, California, February 21-23, 1996, American Metorological Society.

Shabbar, A., 2000: Statistical Approach to Seasonal Forecasting in Canada. In the "Proceedings of the sixth workshop on operational meteorology", Halifax, November 1999, 166.

Shabbar, A. and A. G. Barnston, 1996: Skill of Seasonal Climate Forecasts in Canada Using Canonical Correlation Analysis. Mon. Wea. Rev., 124, 2370-2385.

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