Transformation of the SNOTEL Temperature Record – Methodology and Implications

SNOTEL (SNOw TELemetry) sites collect voltage output data from in-situ temperature sensors (along with other environmental sensors) and transmit these values to the National Water and Climate Center (NWCC) where they are calculated into temperature values using a prescribed algorithm. Beginning in the 1990s, the YSI 44019A thermistor with the 44211A thermilinear package (the extended range YSI temperature sensor) replaced the YSI 44230 temperature sensor as the default temperature sensor deployed at SNOTEL sites because of its broader temperature range. Temperature was calculated from output voltage using a linear least-squares regression developed at the NWCC. There is a step shift in SNOTEL temperature data beginning in the late 1990s, thought to be caused primarily by the switch to the extended-range YSI temperature sensor and the associated algorithm to calculate temperature at SNOTEL sites. A working group within the Natural Resources Conservation Service Snow Survey and Water Supply Forecasting Program conducted an empirical study to characterize the extended range YSI temperature sensor and develop a polynomial algorithm to better calculate temperature from output voltage. The
working group has proposed transforming the historical SNOTEL extended-range YSI sensor temperature record and incoming values using this new algorithm. SNOTEL temperature data is used by many public and private entities in varying ways and transforming the dataset could affect products or management decisions that have already been made. The working group would like to gather feedback from users of SNOTEL temperature data on the implications of transforming the historical dataset and incoming data.