Triggering large avalanches remains likely in wind-drifted snow or on open glades near treeline where a buried weak layer persists. Persistent slab avalanches can travel far and can be difficult to predict, so a conservative approach is recommended.
Ongoing ridgetop winds have redistributed recent low density snow into wind slabs on lee features at upper elevations that remain reactive to human triggering.
A weak layer of surface hoar is buried 80-130 cm deep on sheltered slopes near and below treeline. This layer is likely to be reactive to human triggers in specific areas.
Brrrrrr! Cold and dry conditions persist under arctic air
Sunday night: Partly cloudy, light northwest wind, alpine temperature -18 C.
Monday: Mainly sunny, light northwest wind, alpine high temperature -20 C.
Tuesday: Mainly sunny, light northwest wind, alpine high temperature -23 C.
Wednesday: Mainly sunny, light northwest wind, alpine high temperature -23 C.
Travelers may encounter three different flavors of avalanches on Monday. Expect loose dry avalanches in steep 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.
Over the past 48 hours, numerous large (size 2-2.5) natural, human, and explosive triggered wind slab avalanches have been reported. These avalanches released on north through east through south aspects above 2000 m and broke 30-80 cm deep.
Over the past week, there have been steady reports of large to very large (size 2-3) skier-triggered persistent slab avalanches, failing on a weak layer of surface hoar down 80-130 cm. This MIN report from Friday in the south of the region near Retallack is a helpful example of where this problem exists in the terrain. This MIN report from earlier in the week near Kokanee Pass offers a sobering look at the potential for this problem to propagate widely across features.
Another 10-15cm of snow and moderate ridgetop winds from the northwest have continued to build wind slabs in lee features at upper elevations. With up to 40 cm of low density snow from the past couple days, cohesion-less snow in sheltered areas may be prone to dry loose avalanches that can run far and fast in these cold, dry conditions.
The snow from the past week is settling over a reactive weak layer of surface hoar buried 80-130 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, with much of the notable activity coming from areas south in the region. This layer will be slow to gain strength and requires careful terrain selection.
A less reactive layer of surface hoar or facets buried in early January can be found down 100-160 cm.
The mid/lower snowpack is generally well settled and strong in most areas.
