The SWSI is designed for areas that rely primarily on snowmelt runoff as the primary source of surface water. The SWSI accounts for snowpack, mountain precipitation, streamflow, reservoir contents, and soil moisture conditions. The SWSI can be used by irrigators, fisheries personnel, recreationists, and others who utilize surface waters. SWSI values are categorized as follows:
Extremely Dry: -4.0 to -3.0 Moderate Dry: -2.9 to -2.0 Slightly Dry: -1.9 to -1.0 Near Average: -0.9 to 0.9 Slightly Wet: 1.0 to 1.9 Moderately Wet: 2.0 to 2.9 Extremely Wet: 3.0 to 4.0