Days are short and temperatures are cold! Bring lots of warm layers and keep your objectives conservative and close to home.
Extensive wind effect has been observed in the alpine and exposed treeline. Seek out wind sheltered terrain where you can avoid wind slabs and find great riding.
Northerly outflow winds today may create wind slabs in unusual cross-loading and reverse-loading patterns. This atypical spacial distribution could surprise riders.
On Wednesday night, westerly winds have redistributed available snow and into small pockets of wind slabs in the alpine and treeline with remain possible to be triggered by riders.
A weak layer of facets above a crust that formed in early December is found 70-150 cm deep. While it has become less likely to trigger avalanches on this layer, the consequences are large. The most suspect terrain would be shallow rocky start zones.
The cold before the storm...
Thursday Overnight: Cold and mainly clear. Light northerly winds and alpine temperatures dropping into the -20s C by the early morning.
Friday: Cold and clear. Light northerly winds in the alpine, temperatures increasing throughout the day with an alpine high of -13 C. Strong northerly outflow winds can be expected through the Coquihalla and Allison Pass.
Saturday: Mainly cloudy with flurries. Temperatures increasing throughout the day as a warm front moves into the region, alpine temperatures reaching -10 C. Winds strengthening moderate to strong out of the southwest. Snowfall intensifying overnight, freezing levels rising to 300m with the potential for 10-20cm of accumulation.
Sunday: A stormy day. Strong to extreme southerly winds will accompany another 20-40 cm of new snow accumulation. Freezing levels rising to around 500m.
Earlier in the week, there have been reports of several small (size 1) and a few large (size 2) wind slab avalanches in the Duffey Lakes area. These included natural avalanches on south aspects that were the direct result of reverse loading. With today's northerly outflow winds, we can expect to continue finding reactive wind slabs in unusual locations.
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.
Learn more about how this persistent weak layer is developing in our latest forecaster blog!
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.
This week, variable winds have heavily impacted the snow in open alpine and treeline terrain, leaving wind slabs of a variety of reactivity and hardness on almost all aspects. In some areas, northerly outflow winds throughout the day will redistribute available snow into fresh, more reactive windslabs.
In sheltered areas, it may be possible to find up to 20cm of low density, faceting snow. 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.
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.
