Experimental CCA Forecasts of Canadian Temperature and Precipitation --- Jan–Feb– Mar 2002
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 mb circulation, and the subsequent Canadian surface
temperature and precipitation have been developed. Here, we present the
forecasts for Jan-Feb-Mar 2002 using the predictor fields through November
2001. 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 2002 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. A
large area of eastern and central Canada from Newfoundland through the northern
Prairies including the eastern Arctic is expected to have negative temperature
anomaly. Above-normal temperature anomalies are forecast for the extreme
northwestern regions of Canada. Near-normal values are expected for
southwestern British Columbia.
Figure 3 shows the
CCA-based precipitation forecast for the Jan-Feb-Mar 2002 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 region. With the exception of the lower Great Lakes, the St.
Lawrence Valley and northern Manitoba, above-normal precipitation amounts are
expected throughout most of Canada.
For the most
part, both atmospheric and oceanic indices have been showing ENSO-neutral conditions
for the past several months. Sub-surface temperatures indicate a slow evolution
towards a warm ENSO phase. During the current transition season (Sept- Nov.
2001), intra-seasonal oscillation associated with the westerly wind bursts has
dominated the climate variability in the tropical Pacific. A majority of the
statistical and coupled ocean-atmosphere models indicate a continuation of
neutral conditions in the equatorial Pacific for the 2001-2002 winter. The Jan-Feb-Mar forecast recognizes the prevalence
of ENSO-neutral conditions, as well as
the recent warming trend in northwestern Canada, and their influences on the
Canadian climate over the forecast period.
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 January through March at selected Canadian
stations.
|
Station |
Temp (oC) |
Prcp(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 |
Figure captions:
Fig. 1. (left panel) CCA-based temperature
forecast for the 3-month mean period of Jan-Feb-Mar 2001. Forecasts are
represented as standardized anomalies.
Fig. 2. (right panel) 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. (left panel) CCA-based precipitation
forecast for the 3-month mean period of Jan-Feb-Mar 2001. Forecasts are
represented as standardized anomalies.
Fig. 4. (right panel) 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.
