In the last two issues of this Bulletin, forecasts of Canadian temperature and precipitation using the multivariate statistical technique of canonical correlation analysis (CCA) were presented. For Canada, we have developed the predictive relationships between evolving large scale patterns of quasi­global sea surface temperature, Northern Hemisphere 500 mb circulation, and the subsequent Canadian surface temperature and precipitation. In this issue we present the forecasts for Jul-Aug-Sep 1996 using the predictor fields through May 1996. These forecasts are made with a lead time of 4 months, where lead time is defined as the time between the end of the latest predictor season and the end of the predictand season. Further detail about the Canadian CCA­based seasonal climate prediction is found in Shabbar (1996a, 1996b) and Shabbar and Barnston (1996).

Figure 1 shows the CCA­based temperature forecast for the 3 month period of Jul-Aug-Sep 1996 expressed as standardized anomaly. Table 1 shows the value of the standard deviation in EC at selected stations. The mean skill over all 51 stations is given in the caption beneath each forecast map. The field significance is also shown, reflecting the probability of randomly obtaining overall map skill equal to or higher than that which actually occurred. Field significance is evaluated using a Monte Carlo procedure in which the forecast versus observation correspondences are shuffled randomly 1000 times. The field of cross­validated historical skill (correlation) for the forecast time period is shown in Figure 2. The forecast has a rather limited utility in terms of expected skill, with a mean national score of 0.12. The skill map could not be distinguished from a randomly generated skill map at the 5% level of significance. The skill of the temperature forecast is low during summer in Canada (see the September 1995 issue of this Bulletin, page 28). Locally, modest skills are found over the Great Lakes region and over an area just west of Hudson Bay. Southeastern Ontario and much of arctic Canada are expected to be slightly below normal, whereas temperatures are forecast to be above normal over most of western and south-central Canada.

Figure 3 shows the CCA­based precipitation forecast for the 3 month period of Jul-Aug-Sep 1996 expressed as a standardized anomaly. Table 1 shows the value of the standard deviation (mm) at selected stations. Cross­validated historical skill (correlation) for this time period is shown in Figure 4. The forecast has modest expected skill: a mean national score of 0.10. As with temperature, the skill map does not attain field significance at the 5% level. Local skills are highest over sections of northern Quebec and the western Arctic. The only region showing a spatially extensive anomaly with skill of at least 0.3 is in the Arctic, where an excess of Jul-Aug-Sep precipitation is predicted.

No particularly strong signals are influencing this forecast. Even if the ENSO state were more strongly defined, ENSO is not known to appreciably affect Canadian climate in summer as it is from winter through mid-spring. A gradual historical cooling trend in the north Pacific over the last 15 years would imply a deeper than normal low pressure gyre in the northeastern Pacific and an amplified western Canadian ridge, which would produce warmer than normal temperatures in western Canada.

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

Caveat: This is an experimental product. The Official Environment Canada seasonal forecast can be obtained from the Canadian Meteorological Centre in Montreal.

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. 13th Conference on Probability and Statistics in the Atmospheric Sciences. American Meteorological Society, San Francisco, California, February 21-23, 339-342.

Shabbar, A. and A.G. Barnston, 1996: Prediction of Canadian seasonal temperature and precipitation using canonical correlation analysis. Mon. Wea. Rev.,  124, in press.

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