Trends and variability of snowfall and snow cover across North America and Eurasia. Part 1: data quality and homogeneity analysis

Snow is a significant factor in the national economy and water resources of Northern Hemisphere countries. Snow also has an important role in climatology, both reflecting climatic changes and fluctuations, as well as exerting an influence on climate. The advent of satellite monitoring of weather and climate variables enabled scientists to develop and analyze hemispheric snow cover extent using a consistent database. Unfortunately, the satellite snow record goes back only some four decades. In situ observations of snow cover, as well as snowfall are available for some stations going back to the beginning of the Twentieth Century. The in situ data have been analyzed by several researchers, but these analyses have largely been done independently on regional to national scales. The research presented in this paper and a companion contribution (cf. Robinson and Heim) includes a comprehensive analysis of in situ snow observations from stations in the United States, Canada, and the Former Soviet Union using a consistent methodology applied to all of the stations. This paper discusses the first portion of the effort, and includes: 1) data sources and variables analyzed; 2) the quality control that was applied; 3) the snow indices that were computed from the daily snow observations; and 4) the double-mass analysis that was applied to assess the homogeneity of the data. The quality control, inventory, and homogeneity summary statistics were utilized to identify the best stations to use for Northern Hemisphere snow assessments.