Avoid avalanche terrain Friday. While heavy snowfall and extreme wind ravage the alpine, rain soaks the snowpack below 1800 m.
30-50 cm of heavy new snow in the alpine is being ravaged by extreme wind. A widespread natural avalanche cycle is expected.
Below 1800 m, the snowpack is being soaked by rain. Elevations that have not previously experienced above freezing conditions, or where snow accumulated before turning to rain will be especially susceptible to loose wet avalanche activity.
Significant new loads from snowfall, rain and storm slab avalanche activity Friday will likely overwhelm deep basal weak layers and produce very large, destructive avalanches. These layers do not pose an avalanche problem in the south half of the region.
Thursday night: 10-20 cm new snow, rain below 1200 m. Strong southwest wind, extreme at ridgetop. Freezing level 1200-1500 m.
Friday: 20-30 cm new snow in the alpine, rain line rising to 1800 m by mid afternoon. Extreme southwest wind. Freezing level rising from 1500 to 2100 m.
Saturday: 30-60 cm new snow, rain below 1300 m turning to snow as freezing levels drop. Moderate southwest wind. Freezing level dropping from 1500 m Saturday morning to 500 m by evening.
Sunday: Mix of sun and cloud with flurries bringing up to 5 cm new snow. Moderate southwest wind. Alpine high -5 C. Freezing level valley bottom.
Observations were limited by poor visibility Wednesday, but some natural and explosive triggered storm slab avalanches were observed up to size 2.
Reports of very large (size 3) deep persistent avalanches have been steadily coming in over the past week from the north half of the region. The most recent events occurred on Monday near Goldbridge, Whitecap and Duffey Lake. While most of these events have been naturals on north to east aspects in the alpine, some have been remotely triggered by skiers.
30-50 cm of heavy new snow in the alpine is being ravaged by extreme wind. We suspect scoured windward aspects, hard slab in lee features and rapid cornice growth. Below 1800 m, the snowpack is becoming saturated by heavy rain.
In the north half of the region (ie. Goldbridge/Whitecap/Duffey/Hurley), a few deep instabilities exist in the snowpack, including a weak basal facet crust complex. This has been the failure plane in ongoing reports of deep persistent avalanches. Significant new loads from snowfall and rain will stress the deep basal weakness.
The south of the region, including the Coquihalla and Manning areas, currently have no concerns about deep instabilities.
