Experimental CCA Forecasts of Canadian Temperature

and Precipitation -- Apr-May-Jun 1997

Contributed by Amir Shabbar¹ and Anthony Barnston²

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

amir.shabbar@ec.gc.ca

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 correla-tion 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 Apr-May-Jun 1997 using the predictor fields through February 1997. These forecasts are made with a lead time 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. Further detail about Canadian CCA-based seasonal climate prediction is found in Shabbar (1996a, 1996b) and Shabbar and Barnston (1996).

Figure 1 shows the CCA-based temperature forecast for the 3 month period of Apr-May-Jun 1997 expressed as standardized anomaly. Table 1 shows the value of the standard deviation in C at selected stations. The mean skill over all 51 stations, and the associated field significance, are given in the caption beneath the forecast map. The field of cross-validated historical skill (correlation) for the Apr-May-Jun forecast time period is shown in Figure 2. This forecast has a rather modest mean national score of 0.14. The field significance is 0.082, which falls short of the traditional 0.05 rejection cutoff. 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 skill of the temperature forecast drops off considerably in spring in Canada. Local skill is highest over the northern Canadian prairies, and modest along the west coast. A large area of Canada from the Yukon through the Prairies and into Quebec is expected to have negative temperature anomalies; positive anomalies are forecast over most of British Columbia, southern Ontario and over the high arctic Islands.

Figure 3 shows the CCA-based precipitation forecast for Apr-May-Jun 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 to moderate expected skill, with a mean national score of 0.14 and a barely passable field significance of 0.050. Local skills are highest over sections of the southern Prairies, southwestern British Columbia and the east coast. Much of Canada is expected to have a precipitation deficit in Apr-May-Jun. Exceptions are northern Quebec and parts of the Northwestern Territories.

Many of the statistical and dynamical models are predicting further weakening of the cold conditions in the equatorial Pacific Ocean over the spring season and a possible return toward a weak warm ENSO episode by mid-1997. However, there are wide differences among these model forecasts, reflecting considerable uncertainty as we are now in the "spring barrier". Nevertheless, the Apr-May-Jun forecasts recognize a continuing influence of the 1 to 2-year-long weak to moderate cold event on the spring season Canadian climate. Additionally, this forecast incorporates a component of persistence from the winter circulation pattern, especially over the prairies.

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

Temp Prcp

Station (^oC) (mm)

Whitehorse 1.6 13.2

Fort Smith 2.5 19.5

Innujjuak 1.9 18.2

Eureka 2.6 3.5

Vancouver 1.3 26.6

Edmonton 1.7 26.3

Regina 2.1 30.9

Winnipeg 2.2 37.4

Churchill 2.1 24.6

Moosonee 1.9 27.6

Toronto 1.6 30.0

Quebec City 1.3 35.3

Halifax 1.2 42.7

St. John's 1.6 46.6

Shabbar, A., 1996a: Seasonal prediction of Canadian surface temperature and precipitation by canonical correlation analysis. Proceedings of the 20th Annual Climate Diagnostics Workshop, October 23-37, Seattle, Washington, 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: 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 Apr-May-Jun 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 0.14. Field significance is 0.080.

Fig. 3. As in Fig. 1 (CCA anomaly forecast), except for Apr-May-Jun 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 0.14. Field significance is 0.050 (see text).

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