Meteorological forecasting variables associated with skier-triggered dry slab avalanches

A variety of stability, snowpack and meteorological variables, as well as previous avalanche activity are typically used to forecast the potential for skier-triggered avalanches. However, the relative importance of, and the interaction between, the various variables used to forecast for skier-triggered avalanches have received little attention. This study analyzes the statistical influence of 16 simple meteorological variables, 14 calculated or elaborated variables, and 2 variables for previous skier-triggered avalanche activity at a helicopter skiing operation in the Columbia Mountains of British Columbia, Canada. Forecasting variables are individually assessed using rank correlations to identify the variables most relevant for forecasting the potential for skier-triggered slab avalanches on the regional scale. The variables showing the strongest forecasting potential include: the largest size class of skier-triggered avalanche over the previous one and two days, the 24-h snowfall, the 24-h precipitation, the cumulative storm snow, the height of the snowpack, and the number of days since December 1. The physical processes that relate these variables to skier-triggered avalanches are discussed. The predictive potential of combined forecasting variables is assessed using a multi-variate classification tree model. This model is verified using the last two years of data that was excluded from development of the tree model. The model correctly predicts relatively large avalanches approximately two-thirds of the days for the last two years of the dataset. (C) 2001 Elsevier Science B.V. All rights reserved.