Document Type

Other

Publication Date

2006

Abstract

Snowpack data collection has a long and storied history in Utah as well as the western United States. Many researchers use historical snow course data for various applications ranging from water supply forecasting to climate change. These data are far from a perfect data set and data users should know the errors and limitations within them. In the current setting, only those collecting the data have access to the raw data and the site biographical information. In Utah, records extend back to at least 1912. Systematic measurements began in the mid 1920's with many long term snow courses established at that time. In an extremely fortuitous circumstance, Mr. George D. Clyde (former Governor of Utah) was responsible for the Snow Survey Program during the 1930's in Utah and had foresight to document each existing Snow Course in the year 1936. Each site was meticulously mapped, described and most important, photographed from several angles. Comparisons are made between the 1936 photographs, maps and descriptions and current conditions, specifically with regard to vegetation and sample point location. General conclusions are made regarding the impact that vegetation change has had on snow accumulation at each course. Changes in sampling technique and data processing are documented, particularly with regard to sample density and the re-sampling (or lack thereof in the record up to the 1950's) of individual sample points when density thresholds are exceeded. With the advent of weather modification programs, changes in snow accumulation could reasonably be expected. Utah began a relatively small test weather modification program in the 1950's in central Utah. The Utah cloud seeding act was passed in 1973 and the seeding program has continued since that time. Snow Courses affected by this program are identified and the potential impact on historical data. Finally, recommendations for individual snow course suitability for long term study based on consistency are made for each of the courses examined. SNOTEL sites, the automated version of the snow courses began to be installed in the late 1970's and early 1980's. These sites to a lesser degree due to the shorter historical time of data collection, have been impacted by vegetation change as well. They also have data impacted by sensor changes and weather modification. Because snow course data are often used to extrapolate the SNOTEL data set to a longer time frame, it is important that external influences in this data set are quantified as well.

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