Wind slabs and persistent slabs are becoming less likely to trigger, but conditions still demand assessment of suspect features in wind affected areas and around sheltered openings at lower elevations.
Weather Forecast
Monday night: Mainly clear. Light east winds. Tuesday: Mainly sunny. Light east winds. Alpine high temperatures around -11.Wednesday: A mix of sun and cloud. Light east winds. Alpine high temperatures around -8.Thursday: Cloudy with scattered flurries bringing around 5 cm of new snow, continuing overnight. Light southwest winds. Alpine high temperatures around -10.
Avalanche Summary
Reports from the past couple of days show a continuation of wind slabs reacting to ski cuts, with a trend toward smaller (size 1) releases. Small (size 1-1.5) loose dry avalanches have also been observed releasing naturally from steeper, sun exposed slopes in recent days.On Wednesday, numerous rider triggered wind slab avalanches up to size 2 were reported primarily on northerly aspects at treeline and above. The largest one was a buried, hard wind slab that was sitting on facets on top of a crust. Reports of human triggered persistent slab avalanches on our January weak layers have recently been on the decline, suggesting these layers have evolved into a lower likelihood avalanche problem, but one that still requires a measure of discipline to manage effectively.
Snowpack Summary
Weeks of mainly dry, windy, and cold weather have transformed the snowpack at upper elevations into a mix of wind-affected surfaces and wind slabs of varying ages on all aspects. These wind slabs have shown prolonged reactivity because of the faceted (weak, sugary snow) they overlie. There are a couple of prominent weak layers in the upper snowpack that were buried in mid and late January. These can be found approximately 40-80 cm deep. Both layers consist of surface hoar (weak, feathery crystals) and may be associated with a crust on steep, south facing slopes. These weak layers have been most reactive at lower elevations, and especially below treeline.The lower snowpack is generally considered to be strong, except for shallow, rocky areas where the cold temperatures continue to facet (weaken) the snowpack.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.