Density of new snow in the central Sierra Nevada

The density of newly fallen snow is often assumed to be 100 kg/cu m (10%) so that water equivalent can be estimated from snow depth. Unlike snow in the Rocky Mountains, Sierran snow often falls at near-freezing temperatures, and warmer temperatures could result in snow with a higher density. Three years of replicated snow board measurements were analyzed to determine the effects of air temperature on new snow density. Analysis of 282 replicates showed that, for boards within 5 m of each other, the mean difference was 1.3 kg/cu m. For the 4 years, 403 samples produced a mean new snow density of 120 kg/cu m with a 95 percent confidence interval of 4.8 kg/cu m. The average air temperature was -3.1 degrees C with a standard deviation of 2.6 degrees C, but numerous storms had above-freezing average temperatures. While plots of temperature versus density showed a positive correlation, regression of temperature on density produced a standard error of 38 kg/cu m and a coefficient of determination of only 0.27.