Regions
Northwest Coastal.
Wind slabs have emerged as the primary avalanche problem in the region, but they aren't the only one. Deeper in the snowpack, our persistent slab problem lingers on.
Weather Forecast
Thursday night: Flurries bringing 10-15 cm of new snow. Moderate to strong southeast winds.Friday: Flurries bringing approximately 10 cm of new snow. Moderate to strong south winds. Freezing level to 600 metres with alpine temperatures around -7.Saturday: Mainly cloudy with scattered flurries and a trace of new snow. Light to moderate southwest winds. Freezing level to 400 metres with alpine temperatures around -7.Sunday: Cloudy with scattered flurries and a trace of new snow. Moderate southwest winds. Freezing level to 500 metres with alpine temperatures around -6.
Avalanche Summary
Wednesday's reports include further observations of the widespread natural avalanche cycle that occurred on Tuesday. Natural wet slab avalanches ran up to size 2.5 and loose wet avalanches ran up to size 1.5. Below treeline elevations were especially active in the north of the region. Reports have been limited due to poor visibility and travel conditions.
Snowpack Summary
Recent stormy weather has blanketed the region with storm slabs that are approximately 30-60 cm deep, with much deeper areas where the wind has transported the recent snow. As these slabs have formed a bond to the surface, ongoing winds and light new snow accumulations have seen our primary hazard transition to wind slabs. At treeline and above, new snow and wind have been loading and stressing a weak interface from February composed of facets, crust, and surface hoar buried over a metre deep. This layer was active prior to the storm and remains an ongoing concern. After below zero temperatures on Wednesday night, a surface crust has likely formed over moist or wet snow previously reported at 1100 metres and below.
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.