Mountain Water Supply Forecast Summary

As of May 1, 2005, natural runoff volumes are forecast to be much below average for the Milk River basin, below to much below average for the Oldman River basin, below average for the Bow River basin, and below average to average for the Red Deer and North Saskatchewan River basins for the March to September 2005 period (Table 1). Forecasts are for higher volumes than during the same time period last year in most areas of the North Saskatchewan, Red Deer, and Milk River basins and for the Bow River, but lower than last year in tributaries of the Bow River and most of the Oldman River basin. Forecasts are lower than last month's forecasts for all basins due to much below average precipitation in the mountains during April which generally ranged from 25 to 35% of normal in the North Saskatchewan, Red Deer and Bow River basins, 25 to 80% of normal in the Milk River basin, and 50 to 80% of normal in the Oldman River basin.

Natural flow volumes recorded during the March-April period were above to much above normal in most mountain-fed rivers of the Bow, Red Deer and North Saskatchewan River basins, due mainly to an early start to snowmelt this year. As a result of prior depletion of the snowpack from January rainfall and melting in the Oldman and Milk River basins, and below to much below normal March-April precipitation, natural runoff volumes during the March-April period were below to much below average in most areas of the Oldman and Milk River basins.

Remaining mountain snow accumulations as of May 1, 2005 are generally much below average in the Oldman River basin and the southern half of the Bow River basin. Mountain snowpack conditions elsewhere generally range from below to much below average.

Although snowpack in the Oldman and Milk River basins was severely depleted in January, future precipitation can still heavily influence the May-September forecast runoff. The forecasts described above assume that precipitation over the summer period will be normal. However, if minimal precipitation occurs during the coming months, near record low volumes are possible in these two basins. Conversely, above normal precipitation could yet result in near average runoff volumes in the Oldman River basin. Much above normal precipitation is needed in the coming months to attain average natural runoff volumes in the Milk River basin. Also, reservoirs were able to store some of the early runoff volume in January, and most are currently at above average levels.

Future precipitation could have a major impact on all the water supply forecasts 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.