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, we have developed the 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. In this issue we present forecasts for Jan-Feb-Mar 1997 using the predictor fields through November 1996. These forecasts are made with lead times of 4 months, where lead time is defined here as the time between the end of the latest predictor season and the end of the predictand season. Cross-validation skill scores in historical data indicate that CCA-based seasonal forecasts are most skillful at this time of year. Further detail about Canadian CCA-based seasonal climate prediction is found in Shabbar (1996) and Shabbar and Barnston (1996).

Figure 1 shows CCA-based temperature forecast for the 3 month period of Jan-Feb-Mar 1997 expressed as standardized anomaly. Temperatures are forecast to be near normal to slightly below normal throughout most of the country. Table 1 shows the value of the standard deviation in C at selected stations. The mean skill over all 51 stations is given in the caption beneath the forecast map. The field significance is also shown, The field of cross-validated historical skill (correlation) for the Jan-Feb-Mar forecast time period is shown in Figure 2. This forecast has a mean national score of 0.39 and a "perfect" field significance of 0.000. Field significance reflects the probability of randomly obtaining 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 Jan-Feb-Mar period is the best time to forecast temperature in Canada, and the skill does not deteriorate rapidly as the lead time between the predictor and the predictand time periods is increased out to a year (see Fig. 11-1(a) in the September 1995 issue of Experimental Long Lead Forecast Bulletin). Modest but usable skills are found throughout southern Canada south of the 60 degree latitude. Skill is particularly high over southwestern Ontario.

Figure 3 shows the CCA-based precipitation forecast for Jan-Feb-Mar 1997 expressed as standardized anomaly. Table 1 shows the value of the standard deviation in mm at selected stations. Cross-validated historical skill (correlation) for this time period is shown in Figure 4. The forecast has modest expected skill, with a mean national score of 0.18 and a "perfect" field significance of 0.000. Local skill is highest along the upper Great Lakes and in southeastern British Columbia. Precipitation is expected to be below normal in southern British Columbia and over southern Ontario and southern Quebec. With lower expected skill, an excess in winter precipitation is forecast for the Yukon, the Mackenzie Valley and along the east coast of Canada.

The outlook for April-June 1997 made with a lead time of 7 months (not shown) indicates below normal temperatures from the Yukon through most of the Northwest Territories and northern Prairies into northern Quebec. Only extreme southern Canada is expected to have above normal temperatures. Precipitation for the spring of 1997 is forecast to be above normal from west of Hudson Bay through northern Quebec. Elsewhere, below normal precipitation are expected.

Most of the statistical and dynamical models are predicting further weakening of the cold conditions in the equatorial Pacific Ocean over the fall season and a possible return toward a weak warm ENSO episode by late spring of 1997. The Jan-Feb-Mar temperature forecast shows weak anomalies reflecting an implicitly expected near-normal SSTs in the tropical Pacific. Factors other than the ENSO may also be influencing the Jan-Feb-Mar forecast.

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

Temp Prcp

Station (^oC) (mm)

Whitehorse 5.7 8.6

Fort Smith 4.2 9.1

Innujjuak 3.4 7.4

Eureka 3.5 2.0

Vancouver 1.6 51.9

Edmonton 4.5 10.8

Regina 3.9 9.3

Winnipeg 3.4 11.9

Churchill 3.1 10.1

Moosonee 3.1 18.6

Toronto 2.3 20.7

Quebec City 2.6 35.8

Halifax 2.0 56.7

St. John's 2.5 55.0

Shabbar, A., 1996: 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: Skill of seasonal climate forecasts in Canada using canonical correlation analysis. Mon. Wea. Rev., 124, 2370-2385. Fig. 1. CCA-based temperature forecast for the 3 month mean period of Jan-Feb-Mar 1997. Forecasts are represented as standardized anomalies.

Fig. 2. Geographical distribution of cross- validated historical skill for the forecast shown in Fig. 1, calculated as a 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 0.39. Field significance is 0.000.

Fig. 3. As in Fig. 1 (CCA anomaly forecast), except for Jan-Feb-Mar 1997 precipitation.

Fig. 4. As in Fig. 2 (geographic distribution of correlation skill) except for the precipitation forecast shown in Fig. 3. The mean score over 69 stations is 0.18. Field significance is 0.000 (see text).

[Previous Article] [Next Article]