The recent storm snow combined with strong winds forecast Friday may form reactive wind slabs.
Be mindful of the lingering deep persistent slab problem. Forecast warming temperatures and sunshine this weekend may be enough to wake this problem up and initiate very large avalanches.
Wind slabs may form Friday with strong forecast wind and recent storm snow. They will likely have a poor bond to the crusty snow surfaces.
Dry loose sloughing may be seen from steeper slopes and terrain features.
A deep persistent slab problem formed by a crust down 100-270 cm has created a low likelihood, high consequence scenario that is difficult to forecast. There was an increase in avalanche reports on this deep layer last week but nothing recently with the cool weather.
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 very large and destructive avalanches.
A lot of uncertainty exists with the timing and persistence of the warming that is forecast for Saturday onward.
Friday: Mostly cloudy with no new snow and strong westerly ridgetop winds. Alpine temperatures near -6 and freezing levels at the valley bottom.
Saturday: The region may start to see some warming with the potential for an upper inversion (warmer air aloft 1500-2000m) bringing valley clouds and some sunny skies in the alpine. Alpine temperatures near 0 degrees. Below freezing in the valley bottoms.
Sunday: Mix of sun and cloud with isolated flurries. Ridgetop winds light from the West and alpine temperatures near 0 to -1 if the temperature inversion remains. Freezing levels valley bottom.
On Thursday, skier-controlled and loose-dry avalanches up to size 1.5 were reported.
Wind slabs may form and become reactive on Friday with the new snow and increased ridgetop winds. They may have a poor bond to the underlying crust.
A near-miss happened this weekend on Tombstone mountain when a rider triggered a large persistent slab and got completely buried. Luckily, the airbag helped keep the victim's head above the snow. This evidence suggests the deep persistent slab problem is still a concern in the region.
Up to 15 cm of new storm snow fell Thursday with fairly light winds. Winds are forecast to pick up overnight and into Friday building fresh wind slabs on leeward slopes. Wind slabs may be more reactive where they sit above older wind-affected and crusty surfaces. Around 2000 m and below, a crust caps the dense 15 to 30 cm of snow which has settled significantly with the past mild temperatures. The crust varies from thin and breakable (1800 m and below) to thick and supportive (above 1800 m). Below this, the midpack is well consolidated.
The most notable layer of concern in the snowpack is a crust that was formed in early December and is now down 100-270 cm. This layer was last reactive on Thursday, Jan 13 with warming. This layer has created a tricky low likelihood, high consequence scenario. However, with warm temperatures forecast this weekend we could see this layer wake up and produce very large and destructive avalanches again.
