![]() ![]() As a result, most of the readings from 1878 to 1920 were keyed in manually from the imaged documents-primarily the coldest months, November–April. First, many of the early records are available only as documents since they have yet to be keyed as digital, machine-readable values. What appears to be an opportunity to perform a straightforward assessment of snowfall variations over the past 13 decades, however, runs into additional difficulties-two of which are introduced here. Other regions that were subject to problems are identified and low confidence will be assigned to their results. These issues are largely made moot by the method of analysis described below, as this study eventually describes results for regions containing numerous stations with relatively high snowfall and good record keeping. At low-elevation stations, the observer should have measured the snow at cessation, but we do not have clear documentation that this was always the case. There is some uncertainty about the frequency of measurement for a given 24-h period during which volunteer and/or early observers documented the accumulation through the years. National Weather Service offices (and many other official stations) report snow accumulation (i.e., snowfall) every 6 h to be summed for the daily total, while volunteer observers generally measure the snowfall at cessation for the “greatest accumulation.” Thus, it is very often the case that a 24-h “snowfall” report exceeds the simple difference in depth of snow measured on consecutive days at the official time of observation. This type of measurement, taken in as open an area as possible, minimizes the impacts of melting and compaction. ![]() Note that snowfall is not simply the difference in the “depth-of-snow” measurement on consecutive 24-h periods, but the total accumulation during the previous 24 h. This study addresses the second quantity: total snowfall in the past 24 h. Weather observers report three quantities related to snow: 1) liquid equivalent (i.e., of melted snow), 2) total snowfall in the past 24 h, and 3) depth of snow on ground at time of observation ( Doesken and Judson 1996). Many of these reports, especially since 1920, have been keyed into the climatic database of the National Climatic Data Center (NCDC) and conveniently made available online. ![]() Since 1878, many stations have come (and gone)-operated by volunteer observers, government employees, and private industry-which ostensibly recorded daily snowfall as part of a suite of measurements. Considering the vital importance of snowfall for the natural and human-engineered systems of CA, understanding the long-term variations of this quantity has application to a wide variety of stakeholders. With the advent of regular measurements of snowfall in several California (CA) locations as early as 1878, the opportunity seems possible to examine a record exceeding 130 consecutive snow seasons. ![]() This result encompasses the main snowfall region of the western slope of the Sierra Nevada Mountains. For those regions characterized by consistent monitoring and with the most robust statistical reproducibility, no statistically significant trends in their periods of record (up to 133 years) nor in the most recent 50 years are found. Interpreting linear trends on time series with infrequent large anomalies of one sign (i.e., heavy snowfall years) and unresolved data issues should be done with caution. There were problems with the basic data-the most difficult with which to deal was the increasing presence of “zero” totals that should have been recorded as “missing.” This and other issues reduce the confidence that the regional time series are representative of true variations and trends, especially for regions with few systematically reporting stations. The stations were then subdivided into 18 regions for the construction of representative time series of each area. Over 26 000 of these entries were new relative to the NOAA archive, generally providing data prior to 1920. Most data were accessed through the NOAA archive, but several thousand station months of data were separately keyed in from image files of original documents. Monthly snowfall totals from over 500 stations in California, some of which date back to 1878, are examined. ![]()
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