Some factors that influence the accuracy of water supply forecasting in the intermountain region

Data on precipitation, accumulation and ablation of snow and year long soil moisture records are presented in relation with streamflow from north and south slopes of small drainage basins in the Wasatch Mts. of Utah. The following reasons suggest that the water content of the snow on April 1 may not be a reliable index of water yield in this area; The water content of the soil mantle, which must be raised to field moistures capacity, before water is available for streamflow, varies on April 1 from year to year. The moisture deficit in the mantle may be partly overcome by rainfall before snow begins to accumulate, thus making more of the snowpack water available for streamflow, especially from the South slopes. Spring rainfall (inch for inch) is more effective in generating streamflow than equal amounts of fall storms. Rapid melting of the snow results in greater water yield than slow melting. The data suggests that further study is desired for the location of snow courses.