Frequently Asked Questions on the Environment Canada Long-Range Forecasts
What do we forecast?
The Canadian Meteorological Centre (CMC) of Environment Canada issues seasonal forecast of surface air temperature anomaly and accumulated precipitation anomaly. These anomalies are classified in three categories: below normal, near normal and above normal.
Since December 1, 2011, 3-month average seasonal forecasts of temperature and precipitation, spanning time ranges from 1-3 to 10-12 months into the future, as well as temperature forecasts for the first month, have been produced based on results from two coupled atmosphere-ocean-land physical climate models. The forecasts are presented as anomalies of seasonal (or monthly) mean surface air temperature and of accumulated precipitation amount in the above, below or near normal categories, based on climatological norms for 1981-2010.
The user should keep in mind that the predicted seasonal temperature anomaly is that of temperature averaged over the entire day, rather than of maximum or minimum daily temperature. For example, let's suppose that for a given location, the forecast is for an above normal temperature for spring. If there are more clouds than usual during that particular spring, the maximum temperature will probably be lower than usual (clouds absorb and reflect radiation from the sun). But it is also likely that the minimum temperature will be higher (at night clouds tend to keep heat from the ground from escaping to the upper atmosphere). The mean daily temperature for this season may still be above normal even if the maximum temperature is somewhat colder than normal.
The accumulated precipitation anomaly forecast is the anomaly in total liquid water that reaches the ground. This includes all hydrometeors (snow, rain, drizzle, freezing rain, ice pellets). Therefore, one cannot conclude from these forecasts that there will be more snow in winter for example if the forecast is for above normal precipitation since the precipitation could fall as rain rather than snow. The precipitation forecast does not indicate if there will be more or fewer precipitation events nor if there will be more intense precipitation events. Only the total precipitation anomaly is forecast.
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