The arctic and sub-arctic regions are very suitable for model experimentation because their snow and ice covered surfaces change markedly from season to season. These regions lend themselves well to studies of climatic change because, by changing the surface parametres, it is possible to modify significantly the exchange processes for sensible and latent heat. A numerical model has been designed at McGill University, which can use either synoptic data, grid point data or climatic average data, for the calculation of the various terms in the energy balance. The James Bay region is interesting for studies of this kind, and the paper describes a numerical experiment from that region.