Milk River Basin - Water Supply Forecasts

Recorded March to September 2003 natural runoff volume in the Milk River basin was generally below-average, ranging from 62 to 70% of median and ranging in rank between 20th and 26th lowest on record (Table 2). The monthly natural volume forecasts produced for the Milk River basin were within 14.8% of recorded values, on average, for the March through September runoff period.

With wet conditions entering last winter, initial forecasts were higher in anticipation of normal precipitation this year. Forecasts were lowered in February and March as the snowpack was very low. Forecasts increased substantially in April as a result of snowfall in the headwaters and plains snowmelt volumes both being much-above-normal during March. The forecasts decreased steadily through the summer, however with summer precipitation being much-below-normal in the western side of the basin, volumes ended up outside the forecast probable ranges during several months for Western Crossing and the town of Milk River.

Milk River at Western Crossing

The March to September 2003 recorded natural volume for the Milk River at Western Crossing was much-below-average to below-average at 35,100 dam³ or 62% of median and ranks the twentieth lowest on record (based on the 1931-95 data) (Table 2).

Eight monthly (January to August) natural volume forecasts were produced for the Milk River at Western Crossing for the March to September period. Six of the eight forecasts were higher than the recorded value and two (February and March forecasts) were below the recorded value. This is evident in Figure 1, where the recorded March to September 2003 natural volume for the Milk River at Western Crossing (dark blue line) was below the forecasted values (brown triangles) for six of the eight forecasts. The recorded volume was within the probable range on three (January, February, and March) of the eight forecasts and greater than the reasonable minimum for four (January to April) of eight forecasts.

Forecasts ranged within 11.0% to 30.5% of the recorded volumes, with the best forecast in January. Monthly forecasts were on average within 20.5% of the recorded March to September volume. A recent correction in volume data resulted in 7,000 dam³ less runoff this year. Had the volumes been accurate during our forecasts, seven of eight months (all but July) would have been above the reasonable minimum forecasts, and forecasts would have been within 20.5%, on average, of the recorded March to September volume.

Milk River at Milk River

The March to September 2003 recorded natural volume for the Milk River at Milk River was below-average at 61,400 dam³ or 64% of median and ranks the 23rd lowest on record (based on the 1912-95 data) (Table 2).

Eight monthly (January to August) natural volume forecasts were produced for the Milk River at Milk River for the March to September period. Six of the eight forecasts were higher than the recorded value and two (February and March forecasts) were below the recorded value. Monthly forecasts were on average within 13.0% of the recorded March to September volume. This is evident in Figure 2, where the recorded March to September 2003 natural volume for the Milk River at Milk River (dark blue line) was below the forecasted values (brown triangles) for six of the eight forecasts. The recorded volume was within the probable range on five (all but May, June, July) of the eight forecasts and greater than the reasonable minimum for all eight forecasts. Forecasts ranged within 0.8% to 27.7% of the recorded volumes, with only the August forecast within five percent of the recorded values.

Milk River at Eastern Crossing

The March to September 2003 recorded natural volume for the Milk River at Eastern Crossing was below-normal at 81,900 dam³ or 70% of median and ranks the 26th lowest on record (based on the 1912-95 data) (Table 2).

Eight monthly (January to August) natural volume forecasts were produced for the Milk River at Eastern Crossing for the March to September period. Six of the eight forecasts were higher than the recorded value and two (February and March forecasts) were below the recorded value and were on average. This is evident in Figure 3, where the recorded March to September 2003 natural volume for the Milk River at Eastern Crossing (dark blue line) was below the forecasted values (brown triangles) for six of eight forecasts. The recorded volume was within the forecast probable range on all of the eight forecasts and greater than the reasonable minimum for all of the eight forecasts. Forecasts ranged within 0.5% to 34.4% of the recorded volumes, with the July forecast being the best and four of the eight forecasts within five percent of the recorded values. Monthly forecasts were on average within 10.7% of the recorded March to September volume.