Avoid avalanche terrain Saturday. Significant loading from snowfall, extreme wind and rain will maintain dangerous avalanche conditions through the day. There is potential for very large avalanches to run to valley bottom.
70-100 cm of heavy new snow in the alpine is being ravaged by extreme wind. A widespread natural avalanche cycle is expected to continue through the day Saturday.
Likelihood of loose wet avalanches is decreasing as freezing levels drop through the day. Skier triggered loose wet may still be possible at low elevations Saturday morning.
Significant loading from ongoing from snowfall, rain and storm slab avalanche activity Saturday 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.
Friday night: 30-40 cm new snow in the alpine for most areas, as high as 60 cm for the Coquihalla. Rain below 1300 m. Extreme southwest wind. Freezing level 1500 m.
Saturday: 10-20 cm new snow in the alpine for most areas, as high as 40 cm for the Coquihalla. Rain below 1300 m turning to snow as freezing levels drop. Strong southwest wind easing slightly. Freezing level dropping from 1500 m Saturday morning to valley bottom by evening.
Sunday: Mix of sun and cloud with isolated flurries. Light southwest wind. Alpine high -7 C. Freezing level valley bottom.
Monday: Mix of sun and cloud. Light northwest wind. Alpine high -7 C. Freezing level valley bottom.
No avalanche observations on Friday due to poor visibility during the storm.
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.
By Saturday morning, storm totals are forecast to reach 60-80 cm of heavy new snow, with another 10-20 cm falling though the day. Snow in the alpine is being ravaged by extreme wind. We suspect scoured windward aspects, hard slab in lee features and rapid cornice growth. At lower elevations new snow will overly a crust from the preceding rain as freezing levels drop through the day.
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. The 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.
