Item: Storm and weather factors related to dry slab avalanche activity
Title: Storm and weather factors related to dry slab avalanche activity
Proceedings: Proceedings of the 1998 International Snow Science Workshop, Sunriver, Oregon
Authors: Robert E. Davis, U.S. Army Engineer Research and Development Center, Kelly Elder, Colorado State University, Daniel Howlett, Alta Ski Lift Company, Eddy Bouzaglou, Mammoth Mountain Ski Area
Abstract: Storm cycle factors affect slab avalanche response primarily in terms of loading in starting zones. Wind velocity and supply of transportable snow, relative to terrain, control redistribution and thus potential loading of avalanche slopes. Snow metamorphism in near-surface layers may affect the degree of involvement of old snow in slab avalanches and the rate of bonding between the slab and old snow surface. Early season snow conditions and general loading rate during the season may also affect avalanche response. We evaluated empirical factors that combine wind velocity with new snow amount, describe the potential for near-surface grain growth and provide indices of between-storm snow condition. The importance of different factors was rated in terms of explaining deviance in avalanche activity indices. Avalanche activity indices included maximum size, number of releases and sum of sizes of released avalanches. Ranking and scores for the different factors resulted from classification and regression tree analyses carried out on avalanche observations from Alta, Utah and Mammoth Mountain, California. Time lagged conventional factors describing snowfall and derived wind-drift parameters ranked highest in all tests. Snow drift factors segregated into prominent wind directions showed moderate importance. Among the non-storm factors, the starting snow depth of a particular year ranked highest showing the importance of interannual variability. This was followed by the accumulated vapor pressure difference, which we formulated to describe the potential for near-surface grain growth. The average snow depth increase and other factors followed in importance.
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Keywords: avalanche, avalanche forecasting, snow accumulation, snow cover stability
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