Snow water equivalent (SWE) is a common measurement used to determine the amount of water in snowpack. This is a measurement that is useful to hydrologists and river forecasters. It provides an estimate of how much water is on the ground that can potentially run off into rivers and streams. SWE is especially important in the western United States, where the water available during the summer months comes from the snow that falls during the winter.
One formula to measure SWE is to divide the amount of snow by the amount of snow water. Another is shown on the adjacent illustration.
The adage that “one inch of rain equals 10 inches of snow (1:10)" is a myth! The ratio of rain to snow can vary greatly from as low as 1:4 to higher 1:20.