Mean maximum depth of snow and time of occurrence

The map shows the mean maximum depth of snow in centimetres, the standard deviation of the mean maximum depth of snow, and the mean date of mean maximum depth of snow. The information shown on the map is compiled from 1961 – 1970 snow course data in conjunction with 1955 – 1972 snow depth data. An appreciation of the quantity of snow in storage within a drainage basin during late winter is critical to spring flood forecasting. As well, decisions regarding overland transport and wildlife control can be rationally taken. Snow courses have been established to estimate regional snow depth and water equivalent, but the cover is also measured by all principal meteorological stations and by many climatological stations. The depth is measured either by inserting a graduated probe in a relatively drift-free area or by recording the height of the snow indicated by a stationary object such as a stake positioned in the ground prior to snow accumulation. Since the snow surface is irregular in most areas because of drifting, terrain configuration and forest effects, several measurements are usually required before an average can be estimated. The regularly operated snow course located in a representative area or a terrain of a recognized type yields a better spatial average value than that obtained at an airport meteorological station; but airport measurements have the advantage of being made daily, rather than weekly, semi-monthly, or less frequently, thus facilitating more complete statistical analysis. It was possible to draw on two sources of data to construct the map. One was a 1961-1970 summary of 230 snow courses situated across the country. Secondly, the daily measurements of depth at approximately 500 meteorological stations and the average maximum depth, the standard deviation of the mean, and the mean dates of occurrence were calculated for the period 1955-1972. Both sets of data were plotted on a 1:5,000,000 orographic base map and isolines were interpolated, with precedence being given to the meteorological station data because of the larger number and the associated supplemental information.