South Coast Inland

Conditions are more complicated than meets the eye. Cold temperatures, variable wind loading, and a buried weak layer warrant a cautious approach and diligent decision making.

A low pressure system tracking down the coast Wednesday night will bring a dusting of new snow overnight. High pressure will reestablish on Thursday with a more significant storm in store for the weekend.

Wednesday Overnight: A low pressure system will slide down the coast bringing up to 5 cm of new snow accumulation. This new snow will be accompanied by moderate to strong northwest winds at ridge top and alpine temperatures around -20C. 

Thursday: Snowfall will taper in the early morning. Partially cloudy skies will persist for the day, light northerly winds at ridge top with alpine temperatures around -20 C. 

Friday: A cold and mainly clear day. Light northerly winds with an alpine high of -14 C in the afternoon. High cloud developing in the afternoon. Moderate northerly outflow winds can be expected in the Coquihalla and Allison Pass.

Saturday: The next frontal system will arrive, bringing strong to extreme southwest winds in the alpine, 5-10 cm of new snow throughout the day, and temperatures rising to -8 C in the alpine by the afternoon. Snowfall will continue overnight and into Sunday.

There have been reports of several small (size 1) and a few large (size 2) wind slab avalanches in the Duffey Lakes area over the past few days. These included natural avalanches on south aspects that were the direct result of reverse loading. Based on this pattern, we can expect to find reactive wind slabs in unusual locations over the upcoming days.

Cold temperatures may have made cornices facetted and weak, highlighting the importance of avoiding overhead hazard and giving them a wide berth when travelling at ridge crest. Cornice failures can create a large load on the snowpack and trigger persistent weak layers.

Over the past few weeks, we have been concerned about a potential persistent weak layer in the region. While most of the relevant observations have come from the neighbouring Sea To Sky region, similar types of avalanches were observed in northern parts of the region over a week ago. We suspect it would still be possible to trigger avalanches on this layer in isolated terrain features such as shallow rocky start zones around treeline elevations.

Overnight, light snowfall and moderate to strong westerly winds will have transported available snow into fresh wind slabs in the alpine and treeline. This new snow overlies a weak layer of near-surface facets and in isolated areas surface hoar, formed by the persistent cold temperatures earlier in the week.

This week, variable winds have heavily impacted the snow in open alpine terrain and left wind slabs in atypical locations. It may be possible to find up to 20 cm of low density snow in sheltered areas. 

A recent MIN report from the Duffey found a 40 cm deep surface hoar layer. It was found in sheltered north-facing treeline terrain and was reactive in snowpack tests. There are no other reports of this weakness, so it is most likely a relatively isolated instability.

A weak layer of facets (sugary snow) may be found over a crust that formed in early December (down 70-150 cm). In the neighbouring Sea to Sky region this layer has been particularly reactive at treeline and low alpine elevations, between 1800-2100 m. We have seen a decreasing trend in avalanche activity on this layer as it has transitioned into a tricky low-probability high-consequence problem (see the problem description and travel advice for suggestions).

The lower snowpack is well settled. Snowpack depth at treeline ranges from 160-250cm.

• Be especially cautious near rock outcroppings, on steep convexities and anywhere the snowpack feels thinner than average.
• Recent wind has varied in direction so watch for wind slabs on all aspects.
• Watch for areas of hard wind slab on alpine features.