Regions
Northwest Coastal.
New snow on Friday will add load as well as a layer of complexity to our snowpack. Choose your objectives accordingly.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Friday
Weather Forecast
Thursday night: Flurries delivering 5-10 cm of new snow with moderate to strong southwest winds.Friday: Cloudy with scattered flurries delivering another 5-10 cm of new snow. Winds moderate to strong from the southeast. Alpine temperatures around -5, -14 in the north of the region.Saturday: Mainly cloudy with isolated flurries and a trace of new snow. Winds strong from the east. Alpine temperatures around -10.Sunday: Sunny with cloudy periods and no new snow. Winds moderate to strong from the east. Alpine temperatures around -11.
Avalanche Summary
Reports from Wednesday included a remotely triggered Size 3 persistent slab with a crown depth of 50 cm and width of 150 metres in the Ninginsaw area. This slide ran on a steep southeast facing slope and its failure plane is suspected to be either the December 16 facets or the Christmas surface hoar. On Tuesday, a size 2.0 persistent slab was released by explosives control in the Shames area that was 40-60 cm deep on a E-SE aspect at around 1100 metres. This slab avalanche is suspected to have released on the buried Christmas surface hoar. The natural size 3.5 avalanche that occurred near Ningunsaw on Monday remains notable for releasing on basal facets and running full path.
Snowpack Summary
A layer of surface hoar has been growing on the surface in many areas of the region and will be buried over Thursday night. Below the surface, warm temperatures on Wednesday have likely promoted some strengthening of our recent wind slabs. A similar strengthening effect can be expected - although to a lesser degree - at our Christmas surface hoar layer. Aided by warm temperatures, last week's storm snow has settled a bit more, leaving 35-55 cm in protected areas above the Christmas surface hoar. This week's strong to extreme winds from the north and northeast developed wind slabs above various old surfaces, including our Christmas surface hoar. Slabs failing over this layer will be capable of wide propagations. An earlier weak interface that formed during the early December cold snap can be found in isolated areas buried 100-150 cm deep. This layer consists of preserved surface hoar or weak faceted (sugary) snow. The lower snowpack is well consolidated in deep snowpack areas. In shallow snowpack areas, especially around Ningunsaw, an old rain crust near the bottom of the snowpack has developed weak facets and might be triggerable from a thin or rocky area on a convex slope.
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.