Interannual variations in snowpack in the Rocky Mountains

Unpredictable year to year variations in surface water supplies present substantial challenges to present and potential water managers and users in the West. As a part of a study of climate variations and their effect on Western water supplies, data from USDA Soil Conservation Service snowcourses with continuous data since at least 1951 have been investigated for the entire area from the southern Rockies to the Canadian border. Several characteristics of snowpack variations have been indentified and will be described. Systematic differences in snowpack distribution between wet and dry years will be discussed. Large-scale associations between snowpack, gage precipitation and streamflow will be presented. Reasons for year to year regional flucuations in the ratios of snowpack to precipitation and snowpack to streamflow will be suggested. Finally, apparent long-term trends toward wetter winters in the southern Rockies and drier winters farther north will be assessed in terms of known climatic flucuations.