Avalanche Forecast

A low pressure system tracking down the coast on Wednesday night will bring 5-15 cm of new snow overnight, with highest amounts in coastal areas. 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 10-15 cm of snowfall to coastal areas, with up to 5 cm of accumulation expected further inland. This new snow will be accompanied by moderate to strong northwest winds at ridge top and alpine temperatures around -15C. 

Thursday: Snowfall will taper in the early morning. Skies will clear in the morning with high pressure reestablishing. Moderate northerly outflow winds will develop through coastal inlets. Temperatures dropping overnight into the -20s. 

Friday: A cold and clear day. Light northerly winds with an alpine high of -14 C in the afternoon. High cloud developing in the afternoon.

Saturday: The next frontal system will arrive, bringing moderate to strong southwest winds, 5-15 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.

On Tuesday, numerous natural avalanches and cornice failures up to size 2 where observed in the alpine and treeline on a helicopter flight near Whistler. 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 have the potential to create a large load on the snowpack and trigger deeper persistent weak layers.

Small (size 1) wind slab avalanches were observed on south aspects on Monday as a result of reverse loading from northerly wind. There were also some small human triggered wind slabs over the weekend, including this one from Gin Peak that illustrates how wind patterns earlier in the week have left slabs in atypical locations.

We have been paying close attention to the early December crust, which has formed a persistent weak layer in the region. The last reported avalanche on this layer was on Dec 24, but it produced several notable avalanches around Dec 16 at elevations between 1800-2100 m. 

While we have seen a decreasing trend in avalanche activity since then, the avalanche on the 24th provides a good indication of the type of terrain where this problem could persist. This size 2.5 skier-triggered avalanche occurred on a northwest facing slope around 2100 m in the Blackcomb backcountry, and propagated between some shallowly buried rocks.

Overnight, we received 5-15 cm of new, low density snow. In the alpine and treeline, westerly winds may have redistributed this new snow into fresh wind slabs. 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.

Below this new snow in open areas, a heavily wind effected surface exists comprised of hard wind slabs, sastrugi, and softer pockets of more recent wind loading. In sheltered areas, up to 30cm of low density, facetted snow can be found below the new snow.

A weak layer of facets (sugary snow) can be found over a widespread crust that formed in early December (down 60-200 cm). This layer has been most reactive at treeline and low alpine elevations, between 1800-2100 m.

Although we have seen a decreasing trend in avalanche activity on this layer, it has still produced some notable human triggered avalanches over the past week. This problem is particularly hard to predict and poses a tricky low-probability high-consequence scenario (see the problem description and travel advice for suggestions).

The lower snowpack is well settled. Snowpack depth at treeline ranges from 200-300cm. 

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