Wind slabs have kept avalanche danger heightened at upper elevations and our persistent slab problem will be slow to heal. Conservative terrain selection remains paramount - especially at mid elevations where buried surface hoar exists.
Weather Forecast
Sunday night: Cloudy with clear periods and isolated flurries with a trace of new snow. Light to moderate southwest winds.Monday: Mainly cloudy with isolated flurries and a trace of new snow. Light southwest winds, increasing overnight. Alpine high temperatures around -16. Tuesday: Cloudy with scattered flurries bringing around 5 cm of new snow, continuing overnight. Light southwest winds, increasing to strong in the alpine. Alpine high temperatures around -11.Wednesday: Cloudy with continuing isolated flurries and a trace of new snow, with new snow totals of up to 15 cm. Flurries continuing overnight. Alpine high temperatures around -9.
Avalanche Summary
Another small (size 1) persistent slab was triggered by a skier in the western Flathead on Saturday. The slab was 40 cm deep and released from a northeast aspect at 1800 metres in an area that had not seen recent traffic. Several other small persistent slabs were triggered with ski cuts in the same area.Smaller (size 1-1.5) slabs were ski cut on east aspects at 1700-1800 metres in the Fernie area over the past few days. These slabs were 40 cm deep and described as storm slabs, failing at our most recent new snow interface. Strategies for avoiding this storm slab problem mirror those for avoiding the persistent slab problem that drove our Special Public Avalanche Warning.A 50 cm-deep size 1.5 persistent slab was triggered with a ski cut on Monday. This occurred on a north aspect at 1720 metres in the Fernie area. This is the latest of several recent observations of persistent slab avalanches failing on the persistent weak layer that was buried in mid-January. It was more widely reactive during and immediately after the storm this past weekend. The persistent weak layer producing these avalanches is described in the Snowpack Summary below.
Snowpack Summary
Above 1600 m, 30-40 cm of snow from last weekend has been redistributed by strong winds from both north and south. It may sit on weak and feathery surface hoar crystals in shaded and sheltered areas. Below 1600 m, rain from the same event created a new melt-freeze crust on the surface.Above 1600 metres, the mid-January layer of surface hoar and/or crust is now buried around 40 to 60 cm deep. The surface hoar is found on shaded and sheltered slopes and is most prominent between 1600 m and 1900 m. The melt-freeze crust is found on south aspects at all elevations. Slabs that exist above a combination of surface hoar and crust are likely to be particularly reactive. This layer was the subject of our recent Special Public Avalanche Warning.The remainder of the snowpack is generally well-settled. Thin snowpack areas, such as in the east of the region, may hold weak and sugary faceted grains near the base of the snowpack.
Problems
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.
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.