Depth and DensityThe most important characteristic of snow to water managers and hydrologists is its water content. However, depth is of interest to many people also.
Our data collection equipment measures the weight of the snowpack, and therefore its water content.
DensityNew-fallen snow can range in density depending on the air temperature and intensity of the storm. In California, densities of 12% are common. This means that for every 10 inches of snow that accumulates, it will melt to a pool of water 1.2 inches deep.
After it falls, it settles and compacts. The snowpack gets less and less deep, but the snow doesn't melt or go anywhere. Rather, its density increases. When conditions are cold, such as at high elevations in January, it will compact until its density is around 33%. As time goes on, and more snow falls on top, the snow beneath will further compact. At this point, varying levels in a column of snow will have different densities.
Therefore, snow depth is a fleeting indicator of the snowpack. By obtaining a measure of the water content of the snow, which doesn't change unless more precipitaion occurs or the pack melts, we have a good handle on how the rivers will react in the spring.
DepthBy examining field measurements of depth and water content from the past 90 years, we have a general idea of how deep the snowpack is for a given water content each month.
Snow depths on an average-weather year can be approximated by multiplying Snow Water Content values reported near the first of the each month by the following factor:
January 3.0 February 2.8 March 2.5 April 2.25 May 2.0After May, the snowpack will probably remain at slightly above 50% density as it melts. Rain falling on this ripe snow may accelerate its melt rate, but the intense sunshine of late spring and summer is the principal melting energy source.
California Cooperative Snow Surveys