Oldman River Basin - Water Supply Forecasts

As of May 1, 2004, below-average to much-below-average natural runoff volumes are forecast for the March to September 2004 period in the Oldman River basin, except for the Belly River where much-below-average volume is expected (Table 3a). Current forecasted values for the March to September 2004 period for the Oldman River at Lethbridge would rank 18th lowest in 91-years of record (1912-2001). Current runoff volume forecasts range from 69 to 76% of average, 1 to 2% less than last month's forecasted volumes in the St. Mary and Oldman Rivers, 1% higher in the Waterton River, and similar in the Belly River. April precipitation in southwestern areas of the basin was near-normal, while northern mountain areas recorded approximately 60% of normal precipitation. The March to September 2004 forecast volumes are 3 to 13% higher than those recorded during the same period last year.

The first two months of the forecast period have been completed, with March-April 2004 recorded runoff volumes ranging from 75 to 119% of average. Runoff in the Belly River was above-average, and at all other forecast locations below-average to average. Early melt is especially evident in this basin, as runoff has been better than expected so far and the snowpack has depleted significantly. Current volumes represent approximately 10 to 20% of the volumes forecasted. Recorded volume data is preliminary, due to ice effects, and is subject to change. The remaining volume forecast, which is the March to September 2004 forecast minus the recorded volume to date, is available in Table 3b.