Many previous studies of snow accumulation and ablation have been based on snow course data obtained at monthly intervals, using April 1 snow-water equivalents (SWE) as surrogates for the total seasonal accumulation and for the maximum seasonal snowpack on the ground. This article uses daily snow pillow data to determine how well the April 1 SWEs represent the total accumulation and the maximum snowpack within the entire Rocky Mountain region and in individual subregions. April 1 SWE tends to underestimate the peak SWE by ∼6 cm (12%). April 1 SWE provides a more accurate estimate of the total seasonal precipitation, with mean errors of approximately −1.7 cm (4%) for most of the study area and approximately +2 cm (6%) in the eastern portion. The error incurred by the use of April 1 SWE in the estimation of peak SWE does not vary systematically with elevation, but errors in the estimation of total seasonal precipitation do.
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