Take a cautious approach to wind-loaded areas as recently formed wind slabs may remain reactive to human triggering.
Concern for buried weak layers warrants conservative terrain choices with avoidance of steep and convex slopes.
Recent strong southerly wind and moderate snowfall have formed wind slabs on north-facing terrain. While these newer wind slabs will be the most likely to trigger, old thick wind slabs have been reported on a variety of aspects in alpine terrain.
Triggering persistent slab avalanches remains possible due to several weak layers in the top 30 to 80 cm of the snowpack. Facet layers are the primary concern in alpine terrain, while preserved surface hoar layers are the concern in treeline terrain. Recent observations suggest these layers are gradually strengthening, but are still on the radar of professionals.
As winds picked up on Thursday, several natural and one human-triggered wind slabs (size 1-2) were observed in the alpine.
As it warmed up on Friday, several small (size 1) natural and human-triggered wind slabs were observed in alpine and treeline terrain. Several small (size 1) wet loose avalanches were observed below treeline where the precipitation fell as rain.
Triggering large persistent slab avalanches remains a concern. The most recent report of a persistent slab avalanche was from last Monday when two size 2 persistent slabs were triggered on treeline features in northern parts of the region. These avalanches failed on 30 to 50 cm deep facet layers. Similar avalanches were reported in treeline terrain in southern parts of the region on Dec 29th and 30th.
Recent strong to extreme winds have formed drifts, wind-scoured areas, and wind slabs in alpine terrain and along ridges. The recent 30-40 cm of storm snow continues to settle, with moist snow and crusts possibly forming on some surfaces. Several persistent weak layers may be found in the top meter of the snowpack, including a surface hoar layer buried on Dec 28 (30 to 50 cm deep) and a facet layer buried on Dec 23 (40 to 80 cm deep). These layers are increasing in strength, but could still be possible to trigger in specific areas. In alpine terrain, triggering one of these layers is most likely on steep rocky slopes where they present as facets, while in treeline terrain, they are most likely triggered on convex rolls in open trees where they present as preserved surface hoar.
Saturday night
Cloudy with clear periods and isolated flurries. Alpine temperatures drop to a low of -2 °C. Mostly light ridge wind from the south occasionally gusting to 40 km/h. Freezing level at valley bottom.
Sunday
Cloudy with sunny periods. Alpine temperatures reach a high of -2 °C. Ridge wind east 10-25 km/h. Freezing level rises to 600 metres.
MondayA mix of sun and cloud. Alpine temperatures reach a high of -3 °C. Mostly light ridge wind from the south occasionally gusts to 35 km/h. Freezing level rises to 400 metres.
TuesdayCloudy with sunny periods. Alpine temperatures reach a high of -4 °C. Mostly light ridge wind from the south occasionally gusts to 35 km/h. Freezing level at valley bottom.
More details can be found in the Mountain Weather Forecast.
