A study by the U.S. Geological Survey says the decline can be linked to unusual springtime warming and changes in rainfall patterns.
The warming and snowpack decline are projected to worsen through the 21st century, threatening to put a strain on water supplies.
Runoff from winter snowpack accounts for 60 percent to 80 percent of the annual water supply for more than 70 million people living in the western United States, a USGS release said Thursday.
"This scientific work is critical to understanding how climate change is affecting western water supplies," Secretary of the Interior Ken Salazar said. "It helps land managers adapt to changing conditions on the ground, assists water managers with planning for the future, and gives all of us a better understanding of the real impacts that carbon pollution is having on our resources and our way of life."
Since the 1980s there have been declines in snowpack along the entire length of the Rocky Mountains with unusually severe declines in the north, the study found.
"Over most of the 20th century, and especially since the 1980s, the northern Rockies have borne the brunt of the snowpack losses," said USGS scientist Gregory Pederson, the lead author of the study.
"Most of the land and snow in the northern Rockies sits at lower and warmer elevations than the southern Rockies, making the snowpack more sensitive to seemingly small increases in temperature," he said.