Spatial and temporal variability of Canadian monthly snow depths, 1946-1995

In 1995 the Atmospheric Environment Service of Canada (AES),made a major effort to digitize paper records of daily and weekly snow depth that were not in the Canadian Digital Archive of Climate Data. This resulted in the extension of the snow depth record back to the late 1940s at many stations, and the filling of missing data from a number of stations, particularly in the Arctic. This paper describes the database, the methods used both for quality control and to reconstruct missing data, and presents an analysis of the spatial and temporal characteristics of the data over the 1946-1995 period. Principal component analysis of monthly snow depths revealed that snow depths varied coherently over relatively large regions of Canada, with dominant centres of action located over the West Coast, Prairie, Yukon-Mackenzie, southern Ontario, northern Quebec and Maritime regions. In many cases, nodes of coherent snow depth variations were associated with corresponding nodes of coherent snow cover duration fluctuations, with the two time series exhibiting significant positive correlations. Winter and early spring snow, depths were observed to have decreased significantly over much of Canada in the 1946-1995 period, with the greatest decreases occurring in February and March. These depth decreases have been accompanied by significant decreases in spring and summer snow cover duration over most of western Canada and the Arctic. The snow depth changes were characterized by a rather abrupt transition to lower snow depths in the mid-1970s that coincided with a well-documented shift in atmospheric circulation in the Pacific-North America sector of the Northern Hemisphere.