Water Supply Outlook for Alberta

May 2003

Mountain Snowpack

Mountain snow accumulations as of May 1, 2003 are generally below-average to much-below-average for this time of year, except in the Red Deer River basin and parts of the North Saskatchewan River basin where snowpack is generally above-average. Twenty-eight of thirty-five snow course measurements taken at the end of April range from 75 to 175% of average (Table 1). Depletion of the mountain snowpack has been significant at the other seven locations, which range between 40 and 70% of average. Mountain snowpacks in the province range from third lowest to highest on record for this time of year. The current snowpack is generally much lower than last year at this time but much higher than in 2001, which was the lowest on record in several 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 June.

Ten snow course measurements were taken at the end of April in the Oldman River basin. The snowpack is below-average to much-below-average for this time of year, ranging from 39 to 93% of average (Table 2). Of the five snow courses also measured last month, four show significant melting has occurred since April 1. Snowpacks rank from third to sixteenth lowest in up to 53 years of record. The snowpack is generally much lower than in 2002 and is, on average, similar to 2001.

Thirteen snow course meaurements were done at the end of April in the Bow River basin. Snowpacks range from 43 to 110% of average (Table 3). Melt has been evident at the two snow course locations below an elevation of 6300 feet. A major snowstorm in late April significantly improved the snowpack in the northern half of the basin. Snowpack is generally average in the upper Bow River basin north of Canmore and below-average in the rest of the upper basin, south of Canmore. The May 1, 2003 snowpacks rank from fifth lowest to eighteenth lowest in up to 40 years of record. This year's snowpacks are generally one-and-a-half times as large as the record-lows of May 1, 2001. Last year's snowpack was approximately one-and-a-half times as large as this year's.

Twelve snow courses were performed in the Red Deer, North Saskatchewan, and Athabasca River basins at the end of April, with snowpack measurements ranging from 53% to 174% of average (Table 4). Snowpack in the Red Deer River basin is above-average to much-above-average, and improved by about 20% of average due to heavy April snowfall. In the upper North Saskatchewan River basin snowpack measurements varied widely, from above-average at three locations in the upper Brazeau River basin to generally below-average to average elsewhere. Snowpack in the Athabasca River basin is below-average to much-below-average. Snowpack in these three basins is generally much better than in 2001 and much lower than at this time last year. Snowpack measurements rank from sixth lowest to highest on record in up to 35 years of record. The Limestone snow course, in the foothills of the Red Deer River basin, has much more snow than other areas (174% of average) due to a localized snowfall in early October.

At twelve snow course sites, real-time snow accumulation can be monitored using snow pillows. Snow pillows can be viewed by choosing any southern basin, and snow data, in the two drop down menus at:


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 specific spot. A snow course survey is measured at numerous spots and provides a more representative value of snow in the area. 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. The snow pillow graphs on our website show 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.

Click here to see a map of snow course locations

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