Item: Weather and avalanche forecasting: where do we stand?
Title: Weather and avalanche forecasting: where do we stand?
Proceedings: Proceedings of the 1980 International Snow Science Workshop, Vancouver, BC, Canada
Authors: Knox Williams, USDA Forest Service, Fort Collins, CO
Abstract: Forecasting avalanches requires synthesis of weather and snowpack factors selected from a bewildering array of inputs to solve the day's avalanche forecast problem. In the U.S.A. the forecaster must either have direct access to National Weather Service (NWS) products or be in contact with a meteorologist who can provide weather information. In Canada, the Atmospheric Environment Service provides all weather services. Forecast programs can be conveniently categorized in three groups. First, is the small scale program concerned with an area on the order of 10 kmz . Most ski areas fall into this qroup. Second, is the medium scale program of 102 -103 km2 • Examples include the Alta-Snowbird Little Cottonwood Canyon area of Utah and the Trans-Canada Highway in British Columbia. Third, is the large-scale program of 104 -105 km2 employing central avalanche forecasting. Examples include the warning programs in Colorado, Washington-Oregon, and Alaska. One contrast in these programs is that the smaller the scale of the program, the more specific the forecast. The ski area programs forecast for groups of avalanche paths, whereas statewide programs forecast for entire mountain ranges. Regardless of scale, the forecasters must work with the same inputs. Formal avalanche forecasting in the United States began in the early 1950's with avalanche control programs at Alta, Utahi Berthoud Pass, Coloradoi and Stevens Pass, Washington. At that time, forecasting was (as it still is) by pattern recognition, based more on empirical discoveries than on application of theory. One early outgrowth was Atwater's contributory factors to avalanche formation (Atwater, 1968). Not unexpectedly, many of Atwater's factors were meteorological. The first large-scale avalanche forecasting project began in 1973 when the USDA Forest Service (FS) established the Colorado Avalanche Warning Program (Williams, 1978). In 1978, the FS formally assumed responsibility for the Northwest Avalanche Forecast Program, which had been run for several years under the direction of the University of Washington (LaChapelle et al., 1978). Two new programs, one in Utah and one, in Alaska, will begin in 1980. These programs are based on a 1974 Memorandum of Understanding between the FS and the NWS delineating the responsibilities of the two agencies. The FS supplies and trains the avalanche forecasters, while the NWS supplies the weather information and dissemination network. The avalanche forecasters all have meteorology schooling and/or extensive field experience.
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Keywords: terrain, precipitation, wind, temperature, humidity, radiation
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