Intense wind is causing dangerous avalanche conditions in alpine terrain. Buried weak layers remain possible to trigger on steep and convex slopes.
Extreme southerly wind and moderate snowfall will form wind slabs on north-facing terrain. While these new 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.
Minimal avalanche activity has been reported since Monday, with only a few small (size 1) wind slab avalanches observed when wind speeds increased on Wednesday.
Triggering large persistent slab avalanches remains a concern. The most recent report of a persistent slab avalanche was from 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 last week (Dec 29 and 30).
Strong to extreme wind is forming drifts and wind slabs in alpine terrain and along ridges. Recent 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 metre 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.
Thursday night
Cloudy with flurries starting at midnight and brining 10 cm around Kitimat, 5 cm around Terrace, and less farther north, 50 to 70 km/h wind from the southeast, treeline temperatures around -8 °C.
Friday
Stormy weather with 5 to 10 cm of snow, 60 to 80 km/h wind from the south, freezing level climbs to 700 m with treeline temperatures around -3 °C.
SaturdayCloudy with afternoon flurries bringing 5 to 10 cm of snow, 40 to 60 km/h wind from the southeast, freezing level around 500 m with treeline temperatures around -3 °C.
SundayMix of sun and cloud, no precipitation, 30 to 50 km/h wind from the east, treeline temperatures around -5 °C.
More details can be found in the Mountain Weather Forecast.
