Experimental CCA Forecasts of Canadian Temperature and
Precipitation -- Apr-May-Jun 2000
Amir Shabbar1 and Anthony Barnston2
1Climate Research Branch, Meteorological Service of Canada, Downsview, Ontario, Canada
2Climate Prediction Center, NOAA, Camp Springs, Maryland
Over the past few years, forecasts of Canadian temperature and precipitation using the multivariate statistical technique of canonical correlation analysis (CCA) have been presented in this Bulletin. 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 Apr-May-Jun 2000 using the predictor fields through February 2000. 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 3-month period of Apr-May-Jun 2000 expressed as standardized anomaly. Table 1 shows the value of standard deviation in oC at selected stations. The mean skill over all 51stations 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 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 cross-validated historical skill (correlation) for the forecast time period is shown in Figure 2. The forecast has a modest expected skill: a mean national score of 0.14 and a field significance of 0.082. The skill of the temperature forecast drops off considerably in spring in Canada. Local skills are highest over the northern Canadian Prairies, and modest skill is found on the west coast of Canada. A large area of Canada from British Columbia through central Canada and into Atlantic Canada is expected to have positive temperature anomaly; negative temperature anomalies are forecast over the Northwest and Nunavut Territories.
Figure 3 shows the CCA-based precipitation forecast for the 3-month period of Apr-Jun 2000 expressed as standardized anomaly. Table 1 shows the value of standard deviation (mm) at a selected few stations. Cross-validated historical skill (correlation) for this time period is shown in Figure 4. The forecast has moderate expected skill: a mean national score of 0.14 and a field significance of 0.050. Local skills are highest over sections over northeastern Prairies and over Quebec. Most of southern Canada is expected to have a deficit in Apr-May-Jun precipitation. Northern Quebec and parts of the Northwestern Territories show above normal values.
Both atmospheric and oceanic indices have been showing a moderate strength of the cold phase of ENSO since June 1998 in the tropical Pacific. Most statistical and dynamical models are predicting continuation of a weak cold ENSO episode into early summer. Thereafter, the outlook for ENSO is somewhat uncertain. While some statistical models are forecasting slightly warm conditions by fall, the dynamical model is showing neutral conditions in the tropical Pacific. The Apr-May-Jun 2000 forecast recognizes the historically diminishing influence of the cold event on the Canadian climate from the spring to early summer season. More importantly however, the Canadian CCA forecast incorporates a strong component of persistence from the winter circulation pattern.
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.
Table 1. Standard deviation of temperature (Temp) and precipitation (Prcp) for the 3-month period April through June at selected Canadian stations.
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 |
Captions
Fig. 1. CCA-based temperature forecast for the 3-month mean period of Apr-May-Jun 2000. Forecasts are represented as standardized anomalies.
Fig. 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 0.14. Field significance is 0.08.
Fig. 3. CCA-based precipitation forecast for the 3-month mean period of Apr-May-Jun 2000. Forecasts are represented as standardized anomalies.
Fig. 4. 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 69 stations is 0.14. Field significance is 0.05.
