Experimental CCA Forecasts of Canadian Temperature and
Precipitation - Jul-Aug-Sep 1999
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 years, forecasts of Canadian temperature and precipitation using the multivariate statistical technique of Canonical Correlation Analysis (CCA) were presented in the Experimental Long-lead Forecast 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 Jul-Aug-Sep 1999 using the predictor fields through May 1999. This is a 4-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 Jul-Aug-Sep 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 Jul-Aug-Sep forecast time period at this lead is shown in Fig. 2. The forecast has a modest expected skill - a mean national score of 0.18. The field significance of 0.168, reflecting the fact that the overall map skill can be realized by some random process. 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 followed by spring and early summer even at the 6-month lead-time.
Relatively high local skill is found in the Northwest Territories and over southern Ontario. With the exception of the high Arctic and southwestern Ontario, almost all of the country is expected to have above normal temperatures.
Figure 3 shows the CCA-based precipitation forecast for the Jul-Aug-Sep 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 0.13 and a field significance of 0.471 is considerably poorer than the traditional 0.05 level. Local skills are low throughout most of Canada except in portions of western Manitoba, Cape Breton and the Yukon Territory. The west and the east coast, the high Arctic and central prairies are expected to have above normal precipitation. Elsewhere, normal to below normal amounts are predicted.
Both atmospheric and oceanic indices have been showing continuation of the cold phase of ENSO since August 1998. Statistical and dynamical models are indicating that the moderate strength cold phase of ENSO episode will persist towards the end of 1999. The Jul-Aug-Sep forecast recognizes the La Niña episode, as well as the very strong recent warming trend, particularly in western Canada, and their influences on the Canadian climate over the forecast period.
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 three month period July through September at selected Canadian stations.
| Station | Temp (oC) | Prcp (mm) |
| Whitehorse | 1.3 | 19.2 |
| Fort Smith | 1.5 | 23.9 |
| Innujjuak | 1.6 | 23.1 |
| Eureka | 1.5 | 9.9 |
| Vancouver | 1.0 | 30.2 |
| Edmonton | 1.7 | 34.0 |
| Regina | 1.7 | 30.9 |
| Winnipeg | 1.6 | 40.8 |
| Churchill | 1.4 | 24.1 |
| Moosonee | 1.5 | 33.2 |
| Toronto | 1.4 | 35.1 |
| Quebec City | 1.3 | 45.2 |
| Halifax | 1.0 | 56.6 |
| St. John's | 1.3 | 48.5 |
Figure Captions
Fig. 1. CCA-based temperature forecast for the 3 month mean period of Jul-Aug-Sep 1999. 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 0.18. Field significance is 0.168.
Fig. 3. CCA-based precipitation forecast for the 3-month mean period of Jul-Aug-Sep 1999. Forecasts are represented as standardized anomalies.
Fig. 4. Geographical distribution of cross-validated historical skill for the forecast shown in Fig. 3, 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 0.13. Field significance is 0.471.
