Precipitation and snow water equivalent sensors: an evaluation

Telemetry is a major source of snow water equivalent and precipitation data, but questions remain as to the sensors' accuracy and reliability. Hourly measurements at the U.S.D.A. Forest Service's Central Sierra Snow Laboratory, near Soda Springs, California, provided the basis for a comparison of data from a snow pillow, a precipitation storage gauge, and a weighing rain gauge during water years 1984 and 1985. These data were supplemented with meteorologic data and manual snow measurements for seven events that lasted 6 or 7 days and deposited 5 - 18 cm of moisture. Analysis showed that 2 - 6 hours often passed before the pillow registered new snow and 12 - 48 hours often passed before the total storm amount registered; the 46 cm storage gauge overmeasured while the 20 cm weighing gauge undermeasured; variations in sensor excitation voltages produced 2 cm depth fluctuations; and the storage gauge occasionally registered the bulk of a storm's precipitation 6 - 24 hours after the storm ceased or showed 5 cm increases when no precipitation occurred.