Reactive wind slab may exist on leeward slopes and behind terrain features.
Be mindful of the lingering deep persistent slab problem. Forecast warming temperatures and sunshine this weekend may wake this problem up and initiate very large and destructive avalanches.
Up to 10 cm of new snow and strong wind will build new and reactive wind slabs at upper elevations. They could be poorly bonded to the underlying snow surfaces, like surface hoar and crusts. Be extra cautious in leeward terrain and convex rolls.
A hit of sunshine Friday may trigger loose-dry sloughing from steeper terrain features.
The early December crust can be found 90-160 cm deep. A lot of uncertainty exists around this deep persistent slab problem. There was an increase in avalanche reports on this layer earlier this week but things have tapered off currently.
However, change is in the air and it's going to get WARM this weekend. The warming and sunshine may be enough to wake this layer up and initiate large to very large and destructive avalanches. Smaller avalanches may step-down and trigger this layer.
Friday: Mix of sun and cloud. Ridgetop wind gusty up to 40 km/hr from the West/ Northwest. Alpine temperatures -4 and freezing levels 1200 m.
Saturday: Mix of sun and cloud. Mostly valley cloud due to a temperature inversion. Alpine temperatures near 0 to -1 with freezing levels 1400 m. Ridgetop wind will be moderate from the northwest.
Sunday: Similar to Saturday with continued warm air aloft bringing alpine temperatures to -1 and freezing levels 1600 m. Ridgetop wind moderate to strong from the West.
On Thursday, reactive wind slabs were reported up to size 1.5.
On Wednesday, explosive cornice control triggered isolated wind slabs up to size 2 on the slopes below. These did not pull deeper slabs.
Over the last week, the early December persistent weak layer has produced a few large natural avalanches (2-3) in the center of the region. Explosive controls have also produced a 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, especially moving forward to the weekend.
Widespread surface hoar exists up to 2500 m in sheltered locations.
Last week's storm snow continues to settle at lower elevations while upper elevation snow has been redistributed on lee slopes and open areas at treeline forming reactive wind slabs.
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 to thick, according to the aspect and elevation. Below this, a layer of surface hoar and melt-freeze crusts are found, which seems to be still reactive in isolated areas.
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. This layer was reactive last weekend producing many large size 3 avalanches from all aspects and elevations.
Activity has tapered, however, warming, cornice fall, and human triggers from steep, rocky slopes, with a shallow or thin-to-thick snowpack may wake it up again.
