From AMS Glossary
An established line or transect of measurements of snow water equivalent across a snow field in representative mountainous terrain, where appreciable snow accumulates, to monitor seasonal snowpack.
Although intended to be measured over a distance of several hundred meters, in practice snow courses may consist of four or so individual measurements. The measurements are used for runoff prediction and for assessing the potential for flooding or drought, and they are also used in longer- term climatological studies. Along the snow course, core samples are taken periodically (often monthly) throughout the snow season. Approximately 300 snow courses are operated over the western United States.