An Analysis of the Timing of Snow Course Measurement and the Potential Error Compared to April 1 Measurement in Utah

Snowpack data collection began in an organized fashion in Utah during the late 1920's. The April 1 measurement soon proved to be one of the most important surveys with regard to water supply forecasting. These snow survey data, used historically as April 1 data were seldom actual April 1 measurements rather they were normally sampled at some time prior to April 1, in the latter part of March. In the way that Snow Survey Data were being used, principally in linear regression applications versus accumulated streamflow, this presented little error in the forecasting scheme. However, with the advent of telemetered snowpack information, there exist now two sets of data - those manual sites still measured during the end of March and the SNOTEL or electronic data which are actual April 1 values. The snow course data would underestimate the actual April 1 snowpack compared to the SNOTEL data set, however the magnitude of the error has not been determined. Climate change is being characterized by impacts seen in snowpack. For this type of analysis, the longer the data set, typically the better and more substantial and conclusive the findings. SNOTEL has a relatively short record being installed in the late 70's and early 80's but the snow course data reach back into the 20's, making the analysis far more long term. SNOTEL replaced many of the long term snow courses, thus reducing the pool of available long term data for analysis. This analysis compares the potential error associated with actual measurement timing to April 1 and provides an average correction factor for adjusting long term snow course data to observed SNOTEL data in Utah.