The snowpack isn't a fan of rapid change. Freezing levels jumping 2000 m in a couple of hours on Wednesday is about as rapid as it gets. Hazard from wet loose slides might be the obvious problem, but an increasing likelihood of triggering a persistent slab is the most worrying.
Rider triggerable wind slabs may be found on north and east aspects at treeline and above. Recent extreme winds may have focused slab formation at lower elevations than is typical. Warming will increase the likelihood of triggering slabs in the short term.
30 to 70 cm of snow sits over a facet-crust weak layer combination that is possible to human trigger. Recent observations demonstrate the potential for this problem to be triggered remotely and propagate far and wide.
This layer is most reactive between 1800 and 2000m, potentially due to the presence of surface hoar on the crust, but this layer be found above and below this elevation band. Avoid avalanche terrain at this elevation and be aware of slopes above that could be remotely triggered.
Rapid warming on Wednesday will cause surface layers to lose cohesion and shed from steep slopes. This may occur naturally but is even more likely with a human trigger. Larger releases have potential to trigger destructive persistent slab avalanches, especially around treeline.
Tuesday night: Cloudy with diminishing flurries and a final trace of new snow. Moderate west winds, potentially strong in the alpine. Freezing levels remaining near 1300 metres.
Wednesday: Diminishing cloud, possibly remaining overcast. Light to moderate west winds. Treeline high temperatures around +2 with freezing levels rising to 2700m.
Thursday: Sunny. Light to moderate northwest winds, potentially strong in the alpine. Treeline high temperatures around +1 with freezing levels remaining around 2700 metres.
Friday: Sunny. Light variable winds. Treeline high temperatures around +1 with freezing levels between 2200-2700 metres.
On Saturday in the South Coast Inland region a fatal size 3 (very large) skier triggered avalanche was reported in the Duffey Lake area. It ran on the persistent weak layer from late January described in our snowpack summary. This avalanche was triggered in a upper treeline feature on a northeast aspect and showed significant propagation. Click here to read a more detailed report.
This is the same layer that was responsible for a skier triggered size 2.5 avalanche last week on Rainbow mountain. Several smaller skier triggered avalanches on this layer were also reported throughout the week. Most of the avalanche activity on this layer has taken place between 1800m and 2000m but it can be found above and below this elevation band.
We anticipate a significant increase in the likelihood of avalanches on this layer during the warming pattern from Wednesday onward.
Tuesday's flurries should bring 5-10 cm of new snow to the surface by Wednesday morning, burying heavy wind effect and recent wind slab formations resulting from recent south winds that reached up to 120 km/h on Monday morning. The new snow will bury surface crusts at lower elevations and on solar aspects.
Our problematic January layer of facets on crust is now buried down 30 to 70 cm. This layer is widespread between 1800 m and 2000 m, but may be found just above or below this elevation band. It has produced several human and remote triggered avalanches in the past few days. In sheltered terrain at treeline and above, surface hoar may also be found on this layer and it will certainly promote slab reactivity where it exists.
