Canada is vast, and there are many areas that do not have weather stations. To create a country-wide view of Canada’s weather, a method called interpolation is used.
Interpolation starts with observations at weather stations. For example, here is the average temperature recorded at stations.
Now, although there are gaps between stations, we do know that climate variables change in predictable ways across the landscape. For instance, we know that higher elevations and more northern latitudes are generally colder. Scientists use these facts and others to fill in these gaps, and reconstruct past weather conditions across the entire country.
It was not until the 1950s that the weather station network across Canada became dense enough for gridded datasets to include far northern areas. The interpolation tool used here is called ANUSPLIN. The availability of weather station information determines the robustness of the ANUSPLIN results, which are more reliable in areas that have more stations.
ANUSPLIN data can be accessed on ClimateData.ca by selecting any of the climate variables or indices and then clicking on a grid box on the map. Select “Gridded Historical Data”, and ANUSPLIN data will be displayed in orange for the historical period.