Natural Resources Conservation Service Data Collection Network

The Natural Resources Conservation Service (NRCS) has operated the Federal-State-Private Cooperative Snow Survey Program in the western United States since 1935. Utilizing a network of automated SNOTEL (SNOwpack TELemetry) data collection sites, manual snow courses and storage precipitation gauges, NRCS collects, analyzes, and manages snowpack and climatic data in support of water supply forecasting and other resource management activities.

Initially, over 2000 snow courses were established to collect information on mountain snowpack which provides over 75 percent of the West's water supply. The current network consists of approximately 800 active snow courses. Since the late 1970's, over 600 SNOTEL sites have been installed to enhance the network—in many cases replacing existing snow courses. These remote stations not only provide more timely information, they also offer the opportunity to collect additional data needed for management of our natural resources.

SNOTEL Sites

A standard SNOTEL site consists of a snow pillow, a storage-type precipitation gauge, air temperature sensor, and a small shelter for housing the electronics. Additional parameters such as soil moisture, soil temperature, wind, humidity, and solar radiation are monitored at certain stations for specific applications. SNOTEL sites report on a daily or more frequent basis. The following is an explanation of the standard parameters measured at all SNOTEL sites.

Snow Water Equivalent (SWE): A snow pillow measures the snow water equivalent of the overlying snowpack. Snow pillows are "envelopes" of stainless steel or synthetic rubber (hypalon) containing an antifreeze solution. SWE is calculated by measuring the pressure exerted on these pillows by the weight of the snow. Hypalon snow pillows range in size from 6, 8, 10, or 12 feet in diameter with the larger pillows used in heavier snow accumulation zones. Stainless steel pillows are 4 feet x 5 feet and usually configured in groups of two, three, or four depending on snow depth.

Precipitation: The standard SNOTEL precipitation gauge is designed to store the expected annual precipitation at a specific site. The liquid equivalent (in inches) of rainfall, snow, sleet, or hail is measured by the gauge. The gauge is 12 inches in diameter with an alter shield at the orifice to reduce wind effect on precipitation catch. The height of SNOTEL precipitation gauges is designed to be at least three feet above the maximum expected depth of the snowpack, resulting in total gauge heights of 8, 12, 16, 20, 24, 28, and 32 feet.

Temperature: Daily maximum, minimum, and average ambient air temperatures are collected at each site with a self-aspirating shielded temperature sensor.

Snow Courses

Snow courses are permanently marked locations where snow depth and SWE are measured. Most snow courses consist of five to ten sample points. Individual measurements are averaged to derive one value of snow depth and SWE for each snow course. Typically, snow courses are measured near the first of the month from January to June, with mid-month measurements conducted at some locations.

Manual Precipitation Gauges

Manually measured precipitation gauges have a 6-, 8-, or 10-inch orifice. Most gauges have an alter shield to diminish the wind effect on precipitation catch. The gauges are measured near the end of the month to determine an approximate monthly precipitation total.