On the Predictability of Snow Avalanches

Snow avalanches are generally rare and occasionally extreme events. In the general context of prediction and predictably of extreme events, we will examine whether snow avalanches are predictable based on a few examples of forecasts at different scales. Clearly, avalanche predictability depends on scale. When the regional avalanche danger is High or Very High (Extreme), an avalanche is likely somewhere in the region. However, even at such high danger levels, the release probability in a single avalanche path is well below 50% (typically on the order of 1-10%). This means that a single avalanche is a rare event, which is not predictable even when higher danger levels prevail. At the lower danger levels – relevant for backcountry recreation – the release probability is significantly lower. The low release probability does not mean that the risk is low. Even with low occurrence probability the risk might be too high to be acceptable so that comprehensive preventive measures are required.