TRENDS IN AVERAGE SNOW DEPTH ACROSS THE WESTERN UNITED STATES

A network of cooperative observation stations was used to examine trends in average snow depth across the western United States. This station network includes a greater number of low-to moderate-elevation stations, where the snow is particularly sensitive to temperature changes, than the snow course and SNOTEL datasets used in other studies. Results indicate a widespread decrease in snow depth across the region; 70% of stations with statistically significant trends (p <= 0.5 or p <= 0.10) exhibit negative trends. Elevation is a key factor in explaining the spatial pattern of snow depth trends across the region. The fraction of stations with significant negative trends is greatest (80%) at the lower-elevation stations (<1000 m) and is somewhat less (62%) for stations between 2000 and 3000 m. Pacific climate indices, including the Pacific Decadal Oscillation (PDO) and North Pacific Index (NPI), are shown to have important but spatially varying influences upon average seasonal snow depths.