Liquid water due to melt or rain weakens the snowpack and may cause wet snow avalanches. They generally release naturally and are seldom triggered by skiers or boarders.
Tactics: good timing and trip planning. Wait until good refreeze.
Duration: hours to days
- Overcast skies
- High temperatures /strong solar radiation
- Weak night refreeze
- Deep sinking
- Onset of rain, snowballing, pin wheeling and small wet slabs or loose wet
- When sun is the main cause, distribution is mostly depending on aspect and elevation. Aspect and elevation change along the season. Avalanches often start near dark spots
- All aspects are affected in the event of rain on snow.
- Start early, finnish early
- Wait until having good night refreeze
- Consider avalanche runout zones and the possibility of big natural avalanches
Typical Wet Snow Avalanche Situation
- Rain or melt water flowing into a dry snowpack leading to marked weakening at layer boundaries (rain in midwinter, first heavy melt phase of the snowpack due to solar radiation in March).
- Loss of strength through uniform wetting of the snowpack. Collapse of weakened base layers (spring).
If the snow surface is distinctly refrozen, following a clear night, mostly favourable conditions prevail before midday. Pay attention after midday and generally at any time when the sky is overcast. Pay attention to diurnal variation!
- Warm front creates a typical wet avalanche problem. Initial snow limit is low but usually increases with the arrival of the warm air, and rain on new snow.
- Rain in spring on an isothermal snowpack is usually less effective.
- Take into account previous and expected variations. Cold temperatures prolong the danger. Warm temperatures have a long term stabilizing effect. Particularly repeated warming and cooling cycles.
- Rapid, distinct warming towards 0°C increases instability. Solar radiation significantly warms the surface layers, thereby promoting instability.