Item: Predicting snow layer hardness with meteorological factors
Title: Predicting snow layer hardness with meteorological factors
Proceedings: 2002 International Snow Science Workshop, Penticton, British Columbia
Authors: Mark C. Kozak, Kelly Elder, Karl Birkeland, and Phillip Chapman, Dept. of Earth Resources, Colorado State University, Fort Collins, Colorado, Rocky Mountain Research Station, USDA Forest Service, Fort Collins, Colorado, National Avalanche Center
Abstract: The majority of slab avalanche accidents occur when the victim triggers the slide. Slab hardness is an important property affecting skier-triggered avalanches because hardness partially determines whether sufficient stress reaches the weak layer to cause failure and/or fracture. This study examines how new and old snow layer hardness varies with aspect and which meteorological variables most influence those changes. Slab hardness was measured with a ram penetrometer on north and south aspects from January through March, 2000 at Jackson Hole Mountain Resort and Grand Teton National Park, Wyoming. Continuous weather data were obtained from weather stations at Jackson Hole Mountain Resort. Analyses were carried out on new and older near-surface snow layers. A temperature index was calculated for the south and north aspects to describe the delayed effect of increasing temperature on increasing hardness through sintering, settlement, and densification. The south temperature index, maximum daily temperature, and the interaction between maximum daily temperature and incoming shortwave radiation were the most significant predictors of new snow layer hardness on the south aspect. The north temperature index, maximum daily temperature, and the previous day’s wind speed were the most significant predictors of new snow layer hardness on the north aspect. The temperature index was the only significant predictor of old snow layer hardness on both the north and south aspects. The results of this research suggest that it may be possible to use meteorological factors to predict changes in snow hardness – an important component in predicting skier-triggered avalanches.
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Keywords: skier-triggered avalanches, hardness, temperature index
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