Skier stability index - An additional tool for snow avalanche forecasting in Norway?

Abstract

With more people running to the mountains for skiing backcountry terrain, the need for a good snow avalanche forecast is dire. Todays forecast is based on the weather forecast, snow observations by professional observers and modeled snow data. This thesis will investigating if a stability index can contribute to the current avalanche forecast. Three variatons of Skier stability index (S’) has been calculated for the 21 A-regions used in avalanche foreacsting in Norway. The calculations have been done using three different griddings; full region, deployment areas and point of avalanche. Data sets used are snow data from The Norwegian Water Resources and Energy Directorate (NVE) and meteorological data from MetCoOp Ensemble Prediction System (MEPS) for the avalanche forecasting seasons from 2014-2017 (1st December- 31st May). Success rates of S’ on days where avalanches have been reported where checked to investigate the potential of the index. Versions 1 and 2 (assuming no weak layers in the snowpack) showed low success rate, with highest average of 34 % semi-success (1 <S’ ≤ 1.5). Version 3 (assuming buried surface hoar layer) showed a high success rate (80 %), but also gives false positive on days with no observed avalanches. At present time the index does not contribute to the avalanche forecast because of the low success rates. Further investigations in modifeied ways of using the skier stability index can still be interesting. With an improved avalanche observation record for the latest season (2018), validation of avalanche research will become more reliable.