Quality control of Snotel data

The Snotel (Snowfall Telemetry) network maintained by the USDA Natural Resources Conservation Service is a vital component of the western U.S. water supply forecasting program. About 600 automated sites currently provide daily, and some hourly, data on snow water content, precipitation and temperature. Hydrologic quantities typically extend from the late 1970s and most sites have temperature since the mid 1980s. Working jointly with NRCS, the Western Regional Climate Center has developed methods to screen the data base for impossible, unusual, and missing values, and to provide replacement values whenever possible. A series of single station and then multi-station checks are performed. Comparison stations are from the Snotel, coop, and upper air networks, with provisions for RAWS data when WRCC has a new archive format in place. Test show that Snotel stations are most commonly chosen to supply replacements, but coop and upper air sites also contribute. A large fraction can be estimated to within 5 degrees F, and nearly half to within one degree. A more in-depth examination is performed for historical data, and a less expansive method is used for data coming in daily, involving only the single station and then comparisons with nearby snotel sites. A complication to this process is that edits (on hydro quantities only, except for one state) are being made manually on the central data base from the field offices, so coordination is necessary. The motivation for the project is develop the Snotel data into a research quality data set, develop additional and more detailed climate monitoring products, and improve access. The entire dataset is available at WRCC through the web.