Surface Water Supply Index Maps and Reports
The Surface Water Supply Index (SWSI) is designed for areas that rely on snow melt as the primary source of surface water. The SWSI accounts for snowpack, mountain precipitation, streamflow, reservoir storage, and soil moisture conditions. The SWSI is used by irrigators, fisheries specialists, recreationalists, and others to evaluate current and seasonal surface water supplies. SWSI maps and reports are available for each month from January through October beginning in 1992.
View a map by choosing the month and year of interest from the dropdown box or by selecting from the thumbnails below. Asterisk (*) denotes missing map.
Moderately Dry -2.9 to -2.0
Slightly Dry -1.9 to -1.0
Moderately Wet 2.0 to 2.9