Triggering avalanches remains likely in wind-exposed areas with drifted snow or on slopes with a buried weak near and below treeline. These conditions require careful assessment and cautious terrain selection.
Recent strong winds have redistributed the new snow into reactive wind slabs on lee features at upper elevations that are likely to be human-triggered.
A layer of surface hoar is buried 50-80cm on sheltered slopes near and below treeline. Activity appears to be slowing down on this layer, though it remains reactive to human triggers in specific areas.
Saturday night: Cloudy, isolated flurries with trace accumulations, light northwest ridgetop wind, alpine temperatures dropping to -15 C.
Sunday: Mix of sun and cloud, light northwest ridgetop wind, alpine high temperature -14 C.
Monday: Partly cloudy, light northwest ridgetop wind, alpine high temperature -22 C.
Tuesday: Mainly sunny, light north ridgetop wind, alpine high temperature -23 C.
Three different flavors of avalanches can be expected on Sunday. Loose dry avalanches may be possible in areas where the recent snow has not formed a slab. Although typically small (size 1-1.5), these avalanches pose a serious concern for ice climbers and for people traveling in extreme terrain where the possibility of getting knocked off of your feet has severe consequences. At upper elevations, newly formed wind slabs are expected to be reactive to human triggering. At treeline elevations and below, avalanches may be remotely triggered and break larger than expected on a reactive layer of surface hoar.
On Thursday, operators were able to trigger small (size 1-1.5) avalanches breaking within the recent storm snow with explosives.
On Wednesday, a skier remotely triggered a size 2.5 persistent slab avalanche from a ridgetop near Quartz Creek. This avalanche failed on a weak layer of surface hoar on a slope near treeline. Observers across the region this week reported additional signs of instability on this layer including cracking and whumphing near KHMR and propagation in snowpack tests near Mt. Pat.
5-10 cm of new snow since Friday with moderate to strong northwest winds has formed fresh wind slabs in lee features at upper elevations. In sheltered areas, cohesion-less snow may be prone to dry loose sluffing.
The snow from the past week is settling over a very weak layer of surface hoar buried 50-80 cm deep. This persistent weak layer has potential to surprise backcountry users with how wide the fracture can travel across slopes. Recent avalanches on this layer have primarily been reported at treeline and below. This layer will be slow to gain strength and requires careful terrain selection.
Down 60-100 cm, an older layer surface hoar and/or a thin melt crust from mid January can be found. This layer was more prominent in the north of the region in sheltered, open slopes at treeline.
Deep persistent weak layers can still be found in the lower snowpack. These weak layers are most likely to be triggered from rocky areas with a shallow or thin to thick snowpack.
