Ongoing snowfall in the past week has added significant load to a weak and volatile snowpack.
Reactive storm slabs may be evident underfoot, but keep the potential for large, destructive deep persistent avalanches in the forefront of your mind.
Numerous problematic weak layers exist in the top meter of the snowpack. Recent observations suggest these layers are gaining strength, but we would continue to be cautious around steep openings within and near treeline elevations as active loading continues.
Fresh, reactive storm slabs will build throughout the day with heavy snowfall and strong winds. Storm and wind slab avalanches may step-down to deeper weak layers and initiate large and destructive avalanches.
A layer of large and weak facets sits near the base of the snowpack. This layer is most prominent in upper treeline and lower alpine elevations. Storm slab avalanches could step down to this layer initiating very large avalanches. Riders are most likely to trigger an avalanche on this layer in steep, shallow terrain.
In the Pine Pass area, heavy snowfall caused a natural avalanche cycle that started on Thursday that continued into Saturday morning. Reports from Thursday indicate storm slabs were very reactive to snowmobile traffic, producing many size 1 to 1.5 storm slab avalanches that propagated widely.
With heavy snowfall continuing throughout the day on Sunday, we expect dangerous avalanche conditions to persist. Human-triggered avalanches will be very likely on steep slopes and natural avalanches will likely continue on wind-loaded slopes. Storm slab avalanches could step down to the facets near the base of the snowpack, producing very large avalanches. See more on the potential of triggering deeper weak layers in our latest Forecasters' Blog.
Stormy weather over the past week has brought 40 to 80 cm of new snow to the region. Snowfall will continue throughout the day bringing an additional 10-15 cm. Warm windy weather is causing this storm to settle into reactive slabs. The storm snow sits on previously wind-affected snow. Below this, a melt-freeze crust is found on sun-exposed slopes and everywhere below 1600 m.
Several crust/facet/surface hoar layers exist in the upper and middle portions of the snowpack. Recent observations suggest these layers are gaining strength, but remain on our radar as active loading continues.
The most concerning persistent weak layer is at the base of the snowpack from large and weak facets formed in November. This layer is widespread and most likely problematic in steep, rocky alpine and upper treeline terrain.
Saturday night
Mainly cloudy with flurries, up to 5 cm of accumulation. Alpine temperatures drop to -6 C. Ridge wind southwest 30-70 km/h. Freezing level drops to 1300 m.
Sunday
Cloudy with snowfall, heavy at times, with 10-15 cm of accumulation. Alpine temperatures are around -6 C. Ridge wind southwest 40-70 km/h. Freezing level 1200 m.
Monday
Cloudy with snowfall, up to 10 cm accumulation. Alpine temperatures reach a high of -3 °C. Ridge wind 30 to 80 km/h. Freezing level 1400 metres.
Tuesday
Cloudy with snowfall, heavy at times, with 5-15 cm of accumulation. Alpine temperatures are around -10 C. Ridge wind west 10-30 km/h. Freezing level 1000 m.
More details can be found in the Mountain Weather Forecast.
