Reactive wind slabs remain a concern at upper elevations. If triggered, these slabs can step down to deeper layers, resulting in surprisingly large avalanches.
Wind slab avalanches are possible at upper elevations where wind has blown dry snow into unstable slabs. While these slabs may be thin, they could be poorly bonded to the underlying snow, 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. Although a cooling trend means the snowpack is slowly gaining strength, it is uncertain how the recent warming/rain has affected the snowpack. In the meantime, avoid likely trigger spots such as steep, rocky slopes with a shallow or thin-to-thick snowpack.
SATURDAY NIGHT: Cloudy with flurries, moderate west wind, treeline temperatures around -5 C, freezing level lowering to valley bottom.
SUNDAY: Cloudy, no precipitation, moderate southwest wind increasing all day, treeline temperatures around -6 C, freezing level rising to 1000 m by midday.
MONDAY: Snow 5 cm, strong westerly wind, treeline temperatures around -3 C, freezing level around 1200 m.
TUESDAY: Snow 5 cm, moderate northwest wind, treeline temperatures around -8 C, freezing level returning to valley bottom.
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.
In the center of the region, the early December persistent weak layer produced a natural size 2,5 avalanche lately. Explosive control have also produced few size 2 avalanches that failed on the same persistent weak layer. These occurred on relatively shallow northeast-facing slopes at 2000 m, where the layer was buried 80-120 cm + deep.
We have seen sporadic avalanche activity on this 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 new 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 is continuing to settle with the 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.
