SPATIAL AND TEMPORAL VARIABILITY OF CANADIAN MONTHLY SNOW DEPTHS, 1946-1995

In 1995 the Atmospheric Environment Service of Canada (AES),made a maj or effort to digitize paper records of daily and weekly snow depth tha t were not in the Canadian Digital Archive of Climate Data. This resul ted in the extension of the snow depth record back to the late 1940s a t many stations, and the filling of missing data from a number of stat ions, particularly in the Arctic. This paper describes the database, t he methods used both for quality control and to reconstruct missing da ta, and presents an analysis of the spatial and temporal characteristi cs of the data over the 1946-1995 period. Principal component analysis of monthly snow depths revealed that snow depths varied coherently ov er relatively large regions of Canada, with dominant centres of action located over the West Coast, Prairie, Yukon-Mackenzie, southern Ontar io, northern Quebec and Maritime regions. In many cases, nodes of cohe rent snow depth variations were associated with corresponding nodes of coherent snow cover duration fluctuations, with the two time series e xhibiting significant positive correlations. Winter and early spring s now, 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 m ost of western Canada and the Arctic. The snow depth changes were char acterized by a rather abrupt transition to lower snow depths in the mi d-1970s that coincided with a well-documented shift in atmospheric cir culation in the Pacific-North America sector of the Northern Hemispher e.