Experimental CCA Forecasts of Canadian Temperature

and Precipitation Dec-Jan-Feb 1999

contributed by Amir Shabbar¹ and Anthony Barnston²

¹Climate Research Branch, Atmospheric Environment Service, Downsview, Ontario, Canada

²Climate Prediction Center, NOAA, Camp Springs, Maryland

In the last several issues of this Bulletin, forecasts of Canadian temperature and precipitation using the multivariate statistical technique of Canonical Correlation Analysis (CCA) were presented. For Canada,predictive relationships between evolving large scale patterns of quasi-global sea surface temperature, Northern Hemisphere 500 mb circulation, and the subsequent Canadian surface temperature and precipitation have been developed. Here, we present the forecasts for Dec-Jan-Feb 1999 using the predictor fields through August 1998. This is a 6-month lead forecast. More details about the Canadian CCA-based seasonal climate prediction can be found in Shabbar (1996a, 1996b) and Shabbar and Barnston (1996).

Figure 1 shows the CCA-based temperature forecast for the Dec-Jan-Feb 1999 period expressed as a standardized anomaly. Table 1 shows the value of the standard deviation in ^oC at selected stations. The field of cross-validated historical skill (correlation) for the Dec-Jan-Feb forecast time period at this lead is shown in Fig. 2. The forecast has a modest expected skill - a mean national score of 0.25. The field significance is 0.016, which surpasses the traditional 0.05 rejection cutoff. Field significance reflects the probability of randomly obtaining an overall map skill equal to or higher than that which actually occurred. It is evaluated using a Monte Carlo procedure in which the forecast versus observation correspondences are shuffled randomly 1000 times. The skill of the temperature forecast is highest in winter even at the 6-month lead time.

Local skill is highest from the southern prairies through central Ontario and Quebec into Newfoundland, and over extreme northwestern Arctic Islands. A large area of central and eastern Canada from Manitoba to Atlantic Canada is expected to have negative temperature anomalies; positive temperature anomalies are forecast over the western half of Canada.

Figure 3 shows the CCA-based precipitation forecast for the Dec-Jan-Feb 1999 period, expressed as a standardized anomaly. Table 1 shows the value of the standard deviation (in millimeters) at a selected few stations. The spatial field of cross-validated historical skill (correlation) for this lead and time period is shown in Fig. 4. The forecast has a rather modest expected skill: a mean national score of 0.18 and a field significance of 0.025. Local skills are low throughout most of Canada except over the southern prairies and the extreme northwestern Arctic Islands. Areas near the lower Great Lakes are expected to have above normal precipitation, and this is in keeping with the expectation of La Niña conditions.

Both atmospheric and oceanic indices have been showing development of the cold phase of ENSO since May 1998. Statistical and dynamical models are indicating further intensification of the cold phase of ENSO episode towards the winter of 1998-99, although sea surface temperature anomalies have weakened somewhat in early September from their earlier values. The Dec-Jan-Feb forecast recognizes the La Niña episode, as well as the recent warming trend, particularly in western Canada, and their influences on the Canadian climate over the forecast period.

Table 1. Standard deviation of temperature (Temp) and precipitation (Prcp) for the 3 month period December through February at selected Canadian stations.

References

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

Shabbar, A., 1996b: Seasonal forecast of Canadian surface temperature by canonical correlation analysis. 13th Conference on Probability and Statistics in Atmospheric Sciences. American Meteorological Society, San Francisco, California, Feb. 21-23, 339-342.

Shabbar, A. and A. G. Barnston, 1996: Skill of seasonal climate forecasts in Canada using canonical correlation analysis. Mon. Wea. Rev., 124, 2370-2385.

Captions

Figure 1. CCA-based temperature forecast for the 3 month mean period of Dec-Jan-Feb 1999. Forecasts are represented as standardized anomalies.

Figure 2. Geographical distribution of cross-validated historical skill for the forecast shown in Fig. 1, calculated as temporal correlation coefficient between forecasts and observations. Areas having forecast skill of 0.30 or higher are considered to have utility. The mean score over 51 stations is 0.25. Field significance is 0.016.

Figure 3. CCA-based precipitation forecast for the 3 month mean period of Dec-Jan-Feb 1999. Forecasts are represented as standardized anomalies.

Figure 4 Geographical distribution of cross-validated historical skill for the forecast shown in Fig. 2, calculated as temporal correlation coefficient between forecasts and observations. Areas having forecast skill of 0.30 or higher are considered to have utility. The mean score over 69 stations us 0.18. Field significance is 0.025.