Milk River Basin - Water Supply Forecasts

Recorded March to September 2008 natural runoff volumes in the Milk River basin varied from average at Western Crossing to below to much below average at Eastern Crossing, where it was 30th lowest in 91 years of record (1912 to 2001 data). Runoff in the upper basin was much higher than the middle and lower parts of the basin due to better snowpack and heavier summer precipitation. Natural runoff volumes were between 70% and 78% of median for the Eastern Crossing and the town of Milk River, while at the Western Crossing it was 109% of median (Table 1).

The seven monthly (January to August, excluding June) forecasts of March through September 2008 natural volume produced for the Milk River basin were within 9.3% of recorded values, on average. No forecasts were produced in June this year due to flood events. Large amounts of runoff in May and June resulted in some forecasts issued beforehand (May, and one in April) being low.

Natural runoff volumes measured during the month of September were below average at Milk River (Table 1).

Milk River at Western Crossing

The March to September 2008 recorded natural volume for Milk River at Western Crossing was average at 59,000 dam³ or 109% of average and ranks 38th lowest in 70 years of record (1931-2001 data) (Table 1).

Seven monthly (January to August, excluding June) natural volume forecasts were produced for the March to September 2008 period. Volumes were underestimated in April and May, as the upper quartile forecasts ended up being exceeded when major storms in May and June radically increased runoff volumes. The recorded volume was within the probable range and greater than the reasonable minimum for all other forecasts.

Forecasts ranged within 19.0% to 37.8% of the recorded volumes for the first five monthly forecasts, and 0.9% to 5.4% for July and August's forecasts. The forecasts were on average, within 20.9% of the recorded March to September volume.

Milk River at Milk River

The March to September 2008 recorded natural volume for Milk River at Milk River was below average at 74,200 dam³ or 78% of average and ranks 33rd lowest in 91 years of record (1912-2001 data) (Table 1).

Seven monthly (January to August, excluding June) natural volume forecasts were produced for the March to September 2008 period. Volumes were underestimated in May, as the upper quartile forecast ended up being exceeded when major storms in May and June radically increased runoff volumes upstream. The recorded volume was within the probable range and greater than the reasonable minimum for all other forecasts.

Forecasts ranged within 0.5% to 6.7% of the recorded volumes for all months except May, which was within 16.5%. The forecasts were on average, within 4.7% of the recorded March to September volume.

Milk River at Eastern Crossing

The March to September 2008 recorded natural volume for Milk River at Eastern Crossing was below to much below average at 81,500 dam³ or 70% of average and ranks 30th lowest in 91 years of record (1912-2001 data) (Table 1).

Seven monthly (January to August, excluding June) natural volume forecasts were produced for the March to September 2008 period. Volumes were underestimated in May, as the upper quartile forecast ended up being exceeded when major storms in May and June radically increased runoff volumes upstream. The recorded volume was within the probable range and greater than the reasonable minimum for all other forecasts.

Forecasts ranged within 3.4% to 17.1% of the recorded volumes for the first five monthly forecasts, and 0.0% to 1.2% for July and August's forecasts. The forecasts were on average, within 7.2% of the recorded March to September volume.