Experimental CCA Forecasts of Canadian Temperature and Precipitation --- Jan–Feb– Mar 2004
contributed by Amir Shabbar
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, predictive
relationships between evolving large scale patterns of quasi-global sea surface
temperature, Northern Hemisphere 500 hPa circulation, and the subsequent
Canadian surface temperature and precipitation have been developed. Here, we
present the forecasts for Jan-Feb-Mar 2004 using the predictor fields through
November 2003. 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 Jan-Feb-Mar 2004 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
Jan-Feb-Mar forecast time period at this lead is shown in Fig.
2. The forecast has a good expected skill - a mean national score of 0.39
and a “perfect” field significance is 0.000. 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 forecasts versus observation correspondences are shuffled randomly
1000 times. The Jan-Feb-Mar period is the best time to forecast in Canada. The
skill of the temperature forecast is highest in winter followed by spring and
early summer even at the 6-month lead time.
Local skill is highest from the eastern Prairies to southern Quebec.
The eastern two-thirds of southern Canada from the Rockies to Newfoundland are
expected to have negative temperature anomaly; positive temperature anomalies
are forecast for British Columbia and the high Arctic.
Figure 3 shows the CCA-based precipitation
forecast for the Jan-Feb-Mar 2004 period, expressed as a standardized anomaly.
Table 1 shows the value of the standard deviation (in millimetres) 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 0.18 and a “perfect” field significance of 0.000. Local skills are low
throughout most of Canada except southern Alberta and the upper Great Lakes.
British Columbia, most of southern Prairie provinces, Atlantic Canada and areas
north of the 60oN are expected to have above normal precipitation.
Lower Great Lakes, the St. Lawrence Valley and southern British Columbia will
experience drier than normal Jan-Feb-Mar period.
Both tropical atmospheric and oceanic indices have been showing
ENSO-neutral conditions over the past several months. There is no indication of
large-scale increases or decreases of SST anomalies in equatorial Pacific. A
majority of the statistical and coupled model forecasts indicate ENSO-neutral
conditions for the remainder of 2003 and early 2004. The Jan-Feb-Mar 2004
forecast recognizes the warmer-than-normal SSTs in the North Pacific and the
North Atlantic and their influences on the Canadian climate.
Table 1. Standard deviation of temperature
(Temp) and precipitation (Precip) for the 3-month period January through March
at selected Canadian stations.
Station Temp
(oC) Precip(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
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.
Fig. 1. CCA-based temperature forecast for the 3-month
mean period of Jan-Feb-Mar 2004. 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 0.39. Field significance is
0.000.
Fig. 3. CCA-based precipitation forecast for the
3-month mean period of Jan-Feb-Mar 2004. 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 0.18. Field significance is
0.000.
