Oldman River Basin - Water Supply Forecasts

As of May 1, 2008, natural runoff volumes ranging from below average to average are forecast for the March to September 2008 period for the Oldman, Waterton, Belly, and St. Mary Rivers (Table 3a). Current forecasted values for the March to September 2008 period for the Oldman River at Lethbridge would rank 39th lowest in 91-years of record (1912-2001). Current natural runoff volume forecasts range from 89 to 96% of average. In comparison to April 1 forecasts, this represents a decrease of 1 to 2% of average.

The first two months of the forecast period have been completed, with March-April 2008 recorded natural runoff volumes among the seven lowest in 91 years of record. This is due to much below normal precipitation during March and April and below normal temperatures which resulted in less snowmelt than usual. Recorded volume data is preliminary, due to ice effects, and is subject to change. March-April volumes typically comprise a small portion (approximately 10% on average) of the March to September total. The remaining volume forecast, which is the March to September 2008 forecast minus the recorded volume to date, is available in Table 3b. The forecast is for near average May to September 2008 natural runoff volumes, as mountain snowpack remains average to above average, even at lower elevations.