Wet snow

/Wet snow
Wet snow 2017-10-20T13:20:17+00:00

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

Typical signs:

  • 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
    avalanches

Typical distribution:

  • 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.

Tips:

  • 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!

Rain

  • 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.

Temperature

  • 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.