Triggering large avalanches may be possible in wind-drifted snow or in 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 the low density snow into wind slabs on lee features at upper elevations that may be possible to human trigger.
A weak layer of surface hoar may be buried 60-100cm deep on sheltered slopes near and below treeline. This layer may 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 high temperature -22 C.
Monday: Mix of sun and cloud, light west wind, alpine high temperature -23 C.
Tuesday: Mainly sunny, light northwest wind, alpine high temperature -25 C.
Wednesday: Mainly sunny, light northwest wind, alpine high temperature -25 C.
Three different flavors of avalanches may be possible 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 may 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.
Since Friday, there have been numerous reports of natural and skier-triggered avalanches breaking 10-30 cm deep in the recent storm snow. Several small dry loose avalanches have also been observed.
On Thursday, a large (size 2) skier-triggered persistent slab avalanche was reported near the Gorge area. This avalanche failed on the surface hoar buried 60 cm deep. Over the past week, there have been many reported avalanches on this widespread surface hoar layer throughout this region. Check out these examples from the Gorge and from Corbin Pass.
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 30 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 fast and far in these cold, dry conditions.
The snow from the past week is settling over a reactive weak layer of surface hoar buried 60-100 cm deep. This persistent weak layer has potential to surprise backcountry users with how wide the fracture can travel across slopes. Avalanches on this layer have primarily been reported at treeline and below. Although avalanche activity appears to be decreasing, this persistent weak 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 80-130 cm.
The mid/lower snowpack is generally well settled and strong.
