Manual Snow Monitoring
As part of the Snow Survey and Water Supply Forecasting (SSWSF) Program, the National Water and Climate Center (NWCC) administers a manual snow monitoring program for the western U.S. Manual monitoring consists of monthly snow course measurements and aerial marker observations of mountain snowpack. Map: Snow Courses and Aerial Markers
Snow courses are locations where manual snow measurements are taken during the winter season to determine the depth and water content of the snowpack. Snow courses are permanent locations and represent the snowpack conditions at a given elevation in a given area.
Generally, snow courses are about 1,000 feet (300 meters) long and are situated in small meadows protected from the wind. They consist of a variable number of equally-spaced individual sample points, typically 5 to 10.
Snow surveyors travel to snow courses using skis, over-snow machines, or helicopters. Once onsite, the surveyors use snow samplers at each sample point to measure the depth of the snowpack and then weigh the snow to determine the snow water equivalent. The data collected are then entered into the Water and Climate Information System database.
A surveyor uses a snow sampler at a sample point on a snow course to measure the snowpack depth and water equivalent. The remote location of this snow course requires the use of a helicopter.
Historically, snow course measurements were the first form of snowpack data collection, starting in 1906 when Dr. James Church from the University of Nevada measured a course he laid out on Mt. Rose near Reno. Prior to the 1970s and the inception of the automated Snow Telemetry (SNOTEL) network, snow courses were the primary means of collecting snowpack data. As a result, snow course data records often start earlier than SNOTEL records.
Aerial markers are used to measure the depth of snow. The markers are located in remote locations that are difficult to reach by over-snow travel. They consist of one measuring point marked by a vertical support with crossbars that can be easily observed by aircraft flyover. Surveyors then use an estimated density to calculate snow water equivalent.
Harts Pass aerial marker, Washington