Wet snow (slab avalanches)

The avalanche problem is related to wetting and weakening of the snowpack due to the presence of liquid water. Water infiltrates the snowpack due to melt or rain.
The problem can occur due to rain, sun, warm temperatures or lack of refreezing of the snowpack at night.
Avalanches can vary in size from small to very large. Runout length can be very long with high water content.
Mainly natural release.
Requires a snowpack with clear layering.
The probability for wet slab avalanches is at it's highest at first time wetting of a previous dry layered snowpack occurs.
Predicting the release of wet slab avalanches is difficult. It takes time for the water to penetrate into the snowpack and weaken the slab/weak layers enough for an avalanche to release.

When sun is the main cause, distribution of the problem is mostly depending on aspect and elevation.
All aspects are affected in the event of rain on snow.

Weakening and failure of pre-existing weak layers in the snowpack or release at layer interfaces where water accumulates.
Rain is also an additional load on weak layers.

Avalanches releases at pre-eisting weak layers or in layers where water accumulates.

Possible weak layers:

Hours to days, depending on temperature, precipitation and radiatio.
Rapid loss of stability possible
Especially critical as water infiltrates deeper down for the first time after the snowpack has warmed up to 0 °C.
Natural avalanches can become more likely in the course of the day, depending on aspect (unless rain is dominating factor).

Usually easy to recognize, the snow surface becomes wet.
Onset of rain, snowballing, pin wheeling and small wet slabs or wet loose-snow avalanches are often precursors of natural wet-snow slab avalanche activity.
Deep foot-penetration is another sign of increased wetting.