Regions
Northwest Coastal.
Strong winds have littered exposed areas with wind slabs of varying age and reactivity. Keep your guard up in sheltered terrain - recently buried surface hoar continues to demand conservative terrain selection.
Weather Forecast
Sunday: Mainly sunny. Some valley cloud due to a weak temperature inversion. Light variable winds. Alpine high temperatures of -8. Slightly cooler at lower elevations.Monday: Mainly cloudy with isolated flurries and a trace of new snow. Light southwest winds. Alpine high temperatures of -10.Tuesday: Cloudy with flurries bringing about 3 cm of new snow, increasing overnight. Light to moderate south winds.
Avalanche Summary
Reports from Friday included more extensive observations of a recent natural avalanche cycle that produced numerous storm slab avalanches to size 3. Another round of explosives control southeast of Terrace yielded mostly size 1 loose dry and slab releases, with one size 2 wind slab. An explosives-controlled cornice also triggered a size 2.5 slab down to the base of the snowpack on a confined feature in a thin snowpack area.Explosive control work on Thursday produced very large destructive storm slab results from size 3-4+ on north and south aspects the Skeena corridor, as well as a remotely (from a distance) triggered size 2 storm slab at treeline in the Shames area. On Wednesday and Tuesday we received a reports of a large (size 3-3.5) natural cycle as well as two very large (size 4 and 4.5) natural avalanches that failed in deeply wind-loaded areas. The larger of these occurred near Snowbound Creek west of Terrace on a south aspect at 1400 m and ran full path from ridge top to valley bottom, destroying a significant amount of mature forest beyond its historical trimlines.
Snowpack Summary
Strong outflow winds have been scouring and redistributing recent storm snow accumulations of 50-100 cm into deep wind slabs on a variety of aspects in wind-exposed terrain. In sheltered areas at treeline and below, 20-30 cm of settling snow sits over a layer of surface hoar that was recently reported as reactive to skier traffic. Below this, the interface at the base of the storm snow consists of heavily wind affected surfaces at higher elevations as well as sun crusts or dry facets in sheltered terrain. These two layers are the concerns identified in our persistent slab problem.Another interface composed of sun crust, facets, and more isolated surface hoar can be found about 100-150 cm deep. Deeper in the snowpack, around 150-200 cm down, you'll find a crust/surface hoar layer from January which still has the potential to be triggered from a thin snowpack spot, or with a large trigger like cornice fall. Basal facets may be found near the bottom of the snowpack in colder and drier parts of the region, such as in the far north.
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.