Triggering avalanches is possible at treeline and alpine elevations. A tricky buried weak layer warrants careful terrain selection at these elevations.
Shifting wind over the past few days has left wind slabs in unusual cross-loading and reverse-loading patterns. While these slabs may be difficult to trigger, their atypical spatial distribution could surprise 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.
Cold arctic air will persist until Sunday.
TUESDAY NIGHT: Mostly clear skies, no precipitation, strong wind from the north with gusts to 70 km/h, treeline temperatures drop to -25 C.
WEDNESDAY: Mostly sunny with some afternoon clouds, no precipitation, moderate wind from the northwest with gusts to 60 km/h, treeline temperatures around -20 C.
THURSDAY: Cloudy, light flurries with up to 5 cm of low density snow, light wind from the northwest with some gusts to 40 km/h, treeline temperatures around -15 C.
FRIDAY: Mostly sunny skies, strong wind from the north with gusts to 60 km/h, treeline temperatures around -20 C.
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.
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 and 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.
Northerly winds over the past few days heavily impacted the snow in open alpine terrain and left wind slabs in atypical locations. It may be possible to find 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).
