A snow-profile-based forecasting model for skier-triggered avalanches on surface hoar layers in the Columbia Mountains of Canada

Surface hoar crystals grow on the snow surface and can form a persistent weak layer in the snowpack when buried. Skiers may trigger slab avalanches on such layers. These events can be difficult to forecast. During the winters 1995–2002, measurements of snowpack properties including surface hoar layers were collected at study sites in the Columbia Mountains of western Canada. These data were used to develop an empirical model to forecast the shear strength of buried surface hoar layers. The model, which is based on a snow profile and does not require shear strength measurements, accounts for 72% of the variability in the data. For five independent time series, the model estimates shear strength, on average, to within 22% of measured values within 8 days of the snow profile measurements. The profile-based shear strength model was used to forecast a stability index, which shows promise for forecasting skier-triggered slab avalanches on surface hoar layers in the Columbia Mountains. To further verify the suitability of the stability index, skier-triggered avalanche activity on buried surface hoar layers was correlated with the stability index based on shear frame tests, rather than snow profiles.