Be mindful that reactive wind slabs and deep instabilities are still present. Choose well-supported, low consequence slopes.
Fresh and soft slabs will continue to develop with the forecasted winds and recent snowfalls. Wind slab avalanches are possible at upper elevations, where wind blows dry snow into unstable slabs. While these slabs may be thin, they could be poorly bonded to the underlying snow, like a surface hoar/crust combo, so be extra cautious in lee terrain and convex rolls.
A persistent slab problem formed by a crust down 90-160 cm has created a low likelihood, high consequence scenario that is difficult to forecast. The deeply buried weak layer has produced a number of large and surprising avalanches over the past two weeks. This problem is likely to be triggered on steep, rocky slopes with a shallow or thin-to-thick snowpack. The same feature or path can slide repeatedly when the persistent weak layer is reloaded with new snow.
MONDAY NIGHT: Snow 5 cm, moderate westerly wind, treeline temperatures around -3 C, freezing level lowering to valley bottom.
TUESDAY: Flurries then clearing, moderate northwest wind, treeline temperatures around -6 C, freezing level at valley bottom.
WEDNESDAY: Sunny periods, light north wind, treeline temperatures around -10 C, freezing level at valley bottom.
THURSDAY: Light snow, light southwest wind, treeline temperatures around -6 C, freezing level rising to 1000 m.
Fresh wind slabs have been reactive to riders in the last 24 hours, but with limited propagation. Developing cornices were also observed in the western part of the region.
Over the last three days, the early December persistent weak layer has produced few large natural avalanches (2-2.5) in the center of the region. Explosive controls have also produced few size 2 avalanches that failed on the same persistent weak layer, one being remotely triggered. These occurred on thin to thick features on northeast-facing slopes from between 1600 m and 2000 m, where the layer was buried 100 cm + deep. Although avalanche activity has tapper off, it remains a concern across the region.
A natural cycle occurred Thursday releasing several large natural avalanches (size 2.5): storm slabs in alpine terrain, cornice falls pulling storm slabs, wind slabs, and wet slabs running to valley bottom. Smaller loose avalanches were also triggered by solar input and warm temperatures at lower elevations.
Wind and recent dry snow have created reactive wind slabs on alpine lee slopes and open areas at treeline. Around 1900 m and below, a crust is now capping the dense 10-30 cm of snow which has settled significantly with the past mild temperatures. The crust varies from thin/breakable to thick/supportive, according to the aspects and elevation. Below the recent snow, a layer of feathery surface hoar and melt-freeze crusts are found, which seems to be still reactive in isolated areas. Lower elevations have gone through a melt-freeze cycle.
The most notable layer of concern in the snowpack is a crust that was formed in early December and is now down 90-160 cm. Activity on this layer has been sporadic but has generally been triggered on steep, rocky slopes, with a shallow or thin-to-thick snowpack.
