Water Supply Outlook for Alberta

May 2002

Mountain Snowpack

Snow accumulations in the mountains as of May 1, 2002 are above-average to much-above-average for this time of the year
(Table 1). The headwaters of the Highwood and Kananaskis Rivers have much-above-average snowpack for this time of the year Much-below-normal temperatures combined with above-normal precipitation resulted in an increase in snowpack in many areas. The mountain snowpack is an important source of water supply to reservoirs in the province. Typically the peak snowmelt runoff from the mountain areas occurs in late May or in June.

Twelve snow course measurements were made in the Oldman River basin in late April, with values ranging from 100 to 201% of average (Table 2). Above-normal precipitation in April brought many of the upper elevation stations to above-average values for this time of the year. Most sites in the basin typically begin to melt snow in April but due to cool temperatures, the snowpack continued to accumulate during the month. Snowpack in the headwaters of the Oldman River improved dramatically during April. Five snow courses were measured in the headwaters of the St. Mary River, ranging from 100 to 129 % of average. Snow accumulations are significantly above values observed last year at this time. The beginning of May is normally the end of snow accumulation in the mountains.

Snow water equivalent values on the snow pillow may or may not match the snow course value at a particular location. While snow pillow data is very valuable information, the quantity of snow on the pillow is only representative of the accumulation at that point. In some locations, there can be considerable difference between the snow pillow and snow course values. Factors such as wind and exposure of the site can cause the snow pillow values to be significantly different from the snow course survey. A snow course survey is measured at numerous points and provides a more representative value of snow at that location. The snow pillow graphs on our website shows the daily average snow water equivalent. The monthly snow survey is the average of all measurements conducted within five days of the end of the month. Also, where snow pillow and snow course measurements are available for the same site, snow pillow records tend to be much shorter (10-15 years) in length compared to the snow course sites. As a result, the difference in the average value between the snow pillow and the snow course can be attributed to snow water equivalent being derived two different ways (physically measured compared to an instrument reading), site location and length of data record. In some cases, the values can deviate by 10-20%. Therefore, while snow pillows are excellent for analyzing trends and for monitoring accumulation between snow surveys, snow course values should always be used when considering the quantity of snow at a particular location as they best represent that area.

Fifteen snow course measurements were made at the end of April in the Bow River basin with values ranging from 115 to 209% of average (Table 3). Snow accumulations were above-average during April due to above-normal precipitation and much-below-normal temperatures. In the Highwood and Kananaskis headwaters, snow conditions are much-above-average for this time of the year with most snow courses approaching the historical maximum value. Current snow accumulations at many locations in the Bow River basin are two times the seasonal maximum recorded last year.

Twelve snow course measurements were completed in the headwaters of the Red Deer, North Saskatchewan and Athabasca River basins during the last week of April (Table 4). Snow accumulations ranged from 105 to 162% of average at the twelve sites. Snow conditions improved significantly in the Red Deer basin as a result of above-normal precipitation in April.

Snow course measurements are completed monthly. At twelve of the snow course sites, real-time snow accumulation can be monitored using snow pillows. The snow pillow plots can be found on the department website in the Weekly River Report.

For technical enquires about this web page please contact Alberta Environment - Environmental Management Water Management Operations Branch at AENV-WebWS@gov.ab.ca