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The Canadian Meteorological Centre (CMC) has been producing seasonal outlooks for Canada since September 1995. Four times a year (December 1, March 1, June 1, and September 1), the seasonal anomaly forecasts for 3-month seasons (December-January-February, DJF; March-April-May, MAM; June-July-August, JJA; and September-October-November, SON) are made using two numerical models. The seasonal forecasts result from two 6-member ensembles produced with the CCCma second generation atmospheric general circulation model AGCM2 (McFarlane, et al., 1992) and a reduced-resolution version of the medium-range weather forecast global spectral model (SEF) developed at Recherche en prévision numérique (RPN; Ritchie, 1991). The SEF forecasts are available only for the period MAM, 2003 to DJF, 2003-04. Starting from MAM, 2004 the SEF model is replaced by the Global Environmental Multiscale Model (GEM).

The integrations are initialized from the CMC analyzed data at 1-day intervals preceding the start of the forecast season and are labeled as "Lag 1 day", "Lag 2 day", ..., "Lag 6 day", respectively. The global sea surface temperature anomalies from the CMC assimilation system of the month prior to the forecast period are persisted throughout the 3-month forecast. For more details on the forecasts, please read the following web page: http://meteo.ec.gc.ca/saisons/howto_seasonal_0-3_e.html.

Seasonal ensemble forecasts produced by the two models are provided on a 97x48 Gaussian grid (approximately 3.75° lat x 3.75° long).

The user should be aware that grid box values are not directly comparable to station data. Climate models attempt to represent the full climate system from first principles on large scales. Physical "parameterizations" are used to approximate the effects of unresolved small scale processes because it is not economically feasible to include detailed representations of these processes in present day models. Caution is therefore needed when comparing climate model output with observations or analyses on spatial scales shorter than several grid lengths (approximately 1000 to 1500 km in mid-latitudes), or when using model output to study the impacts of climate variability and change. The user is further cautioned that estimates of climate variability and change obtained from climate model results are subject to sampling variability. This uncertainty arises from the natural variability that is part of the observed climate system and is generally well simulated by the climate models.

Notes/updates:

• Starting from MAM, 2004 the forecasts are made with the GEM model instead of the SEF model.
• Data are made available on March 5, 2003.

References:

McFarlane, N.A., G.J. Boer, J.-P. Blanchet, and M. Lazare, 1992: The Canadian Climate Centre second-generation general circulation model and its equilibrium climate. J. Climate, 5, 1013-1044 (Abstract).

Ritchie, H., 1991: Application of the semi-Lagrangian method to a multilevel spectral primitive-equations model. Quart. J. Roy. Meteor. Soc., 117, 91-106.