New snow overnight will increase storm snow totals to 25-40 cm by Wednesday morning. Strong westerly wind will build slabs which will be reactive to human triggering especially in lee terrain features. A buried weak layer warrants a conservative mindset and terrain use strategy.
A weak layer of surface hoar is buried 50-90 cm deep and is still possible to human-trigger. Over the past week, large avalanches have been observed extensively across the region. The distribution of this problem extends to all aspects and elevations, but north to east aspects near treeline have been a hot-spot for reactivity.
25-40 cm of storm snow combined with strong westerly winds is expected by Wednesday morning. The new snow is not expected to bond well with previous surfaces. Strong westerly winds will build thick slabs on lee features at upper elevations. These wind slabs will be reactive to human triggering.
Tuesday night: Mostly cloudy, 10-15 cm snow, strong westerly wind, alpine high temperature -7 C, freezing level 900 m.
Wednesday: Cloudy with isolated flurries, moderate northwest wind, alpine high temperature -9 C, freezing level 500 m.
Thursday: Mostly cloudy with isolated flurries, moderate west wind, alpine high temperature -6 C, freezing level 500 m.
Friday: Mostly cloudy with isolated flurries, moderate easterly wind, alpine high temperature -12 C, freezing level at valley bottom.
A few natural cornice failures and wind slab avalanches up to size 2.5 were reported on Monday.
Reports of large (size 2-2.5) human-triggered and explosive-triggered avalanches releasing on the February 22 surface hoar layer continued throughout the weekend from operators region-wide. This layer continues to surprise people with remote-triggered activity, wide propagation, and a false sense of stability from unreactive ski cuts or from multiple people moving through the terrain before an avalanche releases. Observations have extended to all aspects and elevations, but north to east aspects near treeline have been a hot-spot for reactivity. Avalanches have also occurred at unusually high elevations for surface hoar, with several cases of wind slabs stepping down in the alpine. While the number of reported avalanches has decreased, the size has increased, with more of the activity releasing size 2+.
New snow and wind on Tuesday may build reactive storm slabs and add a new load to cornices. Shallow storm slab avalanches or cornice falls have the potential to step-down to deeper layers and produce very large avalanches.
A storm moved into the region on Tuesday and is expected to bring 25-40 cm of snow with strong westerly winds by Wednesday morning. The new snow is not expected to bond well with previous surfaces. The new snow will build a slab on lee features at upper elevations, where southwest and west winds transport the snow into deeper, more cohesive drifts.
A widespread weak layer of surface hoar is buried 50-90 cm deep. On solar aspects, this layer may sit over a crust. This persistent slab problem is transitioning into a low probability/high consequence scenario. The snow above the weak layer has increased in depth and slab properties, making avalanches more difficult to trigger and masking obvious clues that the problem is present (i.e. cracking, whumpfing). However, if triggered, avalanches will be large and getting caught could have serious consequences. Managing this problem requires a patient and diligent mindset, implemented by avoiding suspect slopes and maintaining conservative terrain margins. This persistent weak layer will likely pose the threat of a low probability/high consequence avalanche until there is a substantial change in the snowpack. Read more about surface hoar on our forecaster blog.
