Snowpack stability variation at a given avalanche danger level

Abstract: To get a more detailed picture of regional snowpack stability patterns at different danger levels a large scale field study has been performed. At four occasions during the winter 2002 stability data were collected in the region of Davos. During each 1 to 3-day sampling period between 50 and 70 full snow profiles with rutschblock tests were recorded, primarily on shady slopes. At the same time the avalanche danger was estimated based on observations in the field. For analysis the profiles were assigned to one of five stability classes: Very Poor, Poor, Fair, Good, Very Good. Relating the stability to the prevailing (verified) danger level showed distinct patterns of stability. At the danger level Low, 90 % of the profiles were rated as Good, or Very Good, whereas at the danger level Considerable, more than 50 % showed Poor or Very Poor stability. The coefficient of variation was about 20% independent of the danger level. Significant differences in aspect and elevation existed. Some of the variation could be explained by differences in snow depth and snowpack consolidation (ram resistance). Due to the stability variation found verification of avalanche forecasts based on single stability tests is hardly feasible