Snow Water Equivalent (SWE) is a common snowpack measurement used in hydrology and avalanche forecasting. It can be thought of as the depth of water that would theoretically result if you melted the entire snowpack instantaneously.
It is used to describe the amount of water contained within the snowpack as a whole, or in some cases to describe the amount of water deposited as snow during a storm. For example, “Yesterday’s 30 inches of new snow had a SWE of 3.15, almost doubling this season’s total SWE in a 24 hr period.”
In general, dense wet snow has a higher SWE than light dry snow. As such, SWE is an important tool for avalanche forecasters to track, or describe impacts of a particular storm, or set of storms.