Mountain Water Supply Forecast Summary

As of May 1, 2008, below average natural runoff volumes are forecast for this year (March - September 2008) for the North Saskatchewan and Milk River basins and the Bow River at Banff and Calgary. Below average to average volumes are forecast for the Oldman, Highwood and Red Deer River basins, and near average natural runoff volumes are forecast for the Kananaskis - Elbow River area (Table 1). Forecasted volumes have decreased in most basins since the April 1 forecasts were issued, due to below to much below normal precipitation in most mountain areas during April.

Cooler than normal temperatures during March and April resulted in less than average melting of snowpack in southern Alberta. Due to the delayed melt and much below normal spring precipitation, natural runoff volumes recorded for March-April were among the ten lowest in 91 years of record in the Oldman, North Saskatchewan, and upper Bow River basins. In other mountain basins, volumes recorded so far have been below to much below average. Recorded volume data is preliminary, due to ice effects, and is subject to change. March-April volumes are typically a small portion of the yearly total, except in the Milk River basin where they account for approximately 40% of the total.

Remaining mountain snowpack is generally slightly below average in the Highwood and upper Bow River basins, near average in the Kananaskis - Elbow River area and in the Red Deer, North Saskatchewan, and Athabasca River basins, and average to above average in the Oldman and Peace River basins. As a result, natural runoff volumes forecast for the remainder of the year (May - September 2008) are below average for the Bow River at Banff and Calgary, below average to average for the Milk, Highwood, Red Deer and North Saskatchewan River basins, and near average for the Oldman River basin and the Kananaskis - Elbow River area. Significant precipitation of 30 to 80 millimetres (mainly as snow) from May 7 to 9 in much of the Bow and Red Deer River basins should further increase these forecasts next month, depending how much more precipitation occurs during the rest of May. Precipitation in these areas during the first twelve days of May has been generally above to much above normal, except below normal to normal in the mountains upstream of Banff.

Forecasts assume that precipitation over the summer period will be normal. Precipitation will have a major impact on the summer water supply forecast between now and the end of September. Streamflow volume forecasts will be updated monthly until mid-summer. Check our Forecaster's Comments throughout the month for updated information regarding runoff conditions.