Strong wind and recent snow may have formed pockets of reactive wind slab.
Be mindful of the lingering deep persistent slab problem. Forecast warming temperatures and sunshine this weekend may wake this problem up and trigger very large and destructive avalanches.
The recent snow from Tuesday's storm accompanied by strong winds and slight warming have formed new and reactive wind slabs. They could have a poor bond to the crusty snow surfaces below.
Dry loose sloughing may be seen from steeper slopes and terrain features.
The early December crust can be found 80-150 cm deep. A deep persistent slab problem has created a low likelihood, high consequence scenario that is difficult to forecast. There was an increase in avalanche reports on this layer last weekend in the adjacent Flathead-Lizard Region. There have been no recent reports in this region.
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.
A lot of uncertainty exists with the timing and persistence of the warming that is forecast for Saturday onward.
Friday: Mix of sun and cloud with no new snow and strong westerly ridgetop winds. Alpine temperatures near -5 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 to -2 degrees. Below freezing in the valley bottoms.
Sunday: Mix of sun and cloud with isolated flurries. Alpine temperatures near 0 to -1. Ridgetop winds light from the West and freezing levels 1900 m.
No new reports on Thursday.
Recent deep persistent slab avalanches were reported in neighboring regions (Lizard-Flathead and Waterton National Park) over the past week. These human-triggered and natural avalanches failed on the early December crust and showed wide propagation. This evidence suggests the deep persistent slab problem is still a concern in the region, especially through the weekend with warming.
Strong winds have redistributed the recent storm snow onto leeward slopes forming pockets of isolated, stiff wind slabs. The wind slabs may be more reactive where they sit above older hard snow surfaces or crusts that extend to 2100 m. The crust varies from thin (unsupportive below 1800 m) to thick (supportive above 1800 m). Below this is a well-settled mid-pack down to the early December crust/facet interface.
The crust that was formed in early December is now typically down 80-150 cm. In the neighboring Lizard-Flathead region, three very large avalanches were reported on this layer on January 13. 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.
