With newly formed wind slabs and deep persistent problems, it is critical to stay disciplined and choose low consequence, well-supported slopes.
Fresh and soft slabs will develop with the incoming warm and windy storm. 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.
SUNDAY NIGHT: Cloudy, moderate west wind, treeline temperatures around -3C, freezing level rising to 1000 m by midday.
MONDAY: Snow 5-10, strong westerly wind, treeline temperatures around -3 C, freezing level around 1200 m.
TUESDAY: Snow 5-10 cm, moderate northwest wind, treeline temperatures around -8 C, freezing level returning to valley bottom.
WEDNESDAY: Mainly sunny, moderate northwest wind, treeline temperatures around -8 C, freezing level at valley bottom.
In the center of the region, the early December persistent weak layer has produced a natural size 2,5 avalanche recently. Explosive control 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.
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.
We have seen sporadic avalanche activity on the persistent weak layer since Jan 4. These have included some large human-triggered avalanches, such as this size 3.5 avalanche just outside the region at Pedley Pass on Jan 4 and this avalanche near Golden on Jan 9, as well as large natural avalanches like this one reported in the South Purcells on Jan 9. These avalanches suggest the persistent slab problem is an ongoing concern in the Purcells.
Recent wind and dry snow (5-15 cm) 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 and snow is still from warming/rain event.
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.
