Globally, long term declines in mountain snowpack have been observed and are further projected over the past three decades, particularly at lower, warmer elevations.  Increasing air temperature in mountainous regions will raise snow lines and major reductions in snow cover are projected for mid-latitudes in general by the end of this century with lower, warmer elevations most affected.  In the U.S., the duration of snow cover has been decreasing by 2-3 days per decade, especially in the western U.S. and during the spring, during the past 28 years. Projected warming in the western mountains by the mid-21st century is very likely to cause large decreases in snowpack, earlier snow melt, more winter rain events, increased peak winter flows and flooding, and reduced summer flows.

Source: Intergovernmental Panel on Climate Change (2007). Fourth Assessment Report (AR4). Intergovernmental Panel on Climate Change.