The Relation of Crystal Riming to Avalanche Formation in New Snow

New snow avalanches are forecast by a study of contributory snow and weather factors. This method can be refined by considering effects of riming on snow crystal types and its variation during storms. Rimefree crystals form unstable snow layers which avalanche readily. Partial riming leads to greater initial stability, but this can allow dangerously thick snow layers to accumulate before a soft slab is released. Thick layers of graupel have a peculiar disposition to form slab avalanches due to the high density and large effective grain size. The empirical basis for these conclusions is illustrated by examples from storm and avalanche case histories. Theoretical speculation is developed to account for these effects of snow crystal riming in terms of the sintering process.