Wind slabs are likely to be encountered at upper elevations and may be reactive to human triggering, especially in lee features.
Weather Forecast
THURSDAY NIGHT - Mainly cloudy with isolated flurries / southwest winds 20-40 km/h / alpine low temperature near -13FRIDAY - A mix of sun and cloud with isolated flurries / southwest winds 10-25 km/h / alpine high temperature near -10SATURDAY - A mix of sun and cloud / northwest winds 10-15 km/h / alpine high temperature near -10SUNDAY - Sunny with cloudy periods / northwest winds 10-15 km/h / alpine high temperature near -8
Avalanche Summary
On Wednesday there were reports of several size 1 loose snow avalanches from steep terrain.On Tuesday, there were two reports of human triggered persistent slab avalanches that failed on the early February persistent weak layer (described in more detail in the Snowpack Summary). These were size 1 and 1.5, on west aspects.In recent days, there have been reports of size 1-1.5 wind slab avalanches on a variety of aspects in the alpine and at treeline, as well as size 1-1.5 loose snow avalanches, primarily on sun exposed slopes.Reports of persistent slab avalanches are becoming less frequent, suggesting our January/February weak layers have evolved into a lower likelihood/high consequence avalanche problem that still requires a measure of discipline to manage effectively.
Snowpack Summary
Approximately 5 cm of new snow is sitting on wind slabs, facets (sugary snow) and surface hoar (feathery crystals) in most areas, and a crust on sun exposed slopes. There are up to three layers of surface hoar that were buried in mid and late January, and early February. These layers are around 30 to 80 cm deep and are most prominent at lower elevations - especially below treeline. The surface hoar may sit on a crust on south facing slopes.The base of the snowpack is composed of weak and sugary faceted grains that sit on a crust. This weak layer has produced large and destructive avalanches that are sporadic in nature and difficult to predict. See the Forecasters' Blog here for more information on this problem. Continued cold temperatures have been weakening the lower 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.