Strong winds are transporting new snow into deep, cohesive slabs at treeline and alpine elevations. Avoid lee and cross-loaded terrain. Minimize exposure to avalanche terrain during times of heavy loading from wind and new snow.
In all exposed areas, new snow and strong southwesterly winds are building deep pockets in lees that are reactive to natural and human triggers. Avoid lee and cross-loaded slopes.
If triggered wind slab avalanches may step-down to deeper weak layers and initiate large and destructive avalanches.
Recent large persistent slab avalanche observations are strong evidence that these layers are still an active concern in this region. Numerous problematic weak layers exist in the top meter of the snowpack. Be cautious around steep openings within and near treeline elevations as active loading continues.
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. Riders are most likely to trigger an avalanche on this layer in steep, shallow terrain. This layer has recently produced very large natural avalanches see avalanche summary for more information. Your best defence is to stay diligent in choosing low-consequence terrain away from overhead exposure.
On Wednesday, a few natural size 3.5 avalanches were observed in wind-loaded alpine features.
On Tuesday, a skier accidental, size 1.5 storm slab avalanche was reported at 1500 m. A size 2, natural windslab avalanche was observed on a northwest aspect at 1400 m.
On Sunday, three very large natural avalanches were observed up to size 4. Two were size 3 persistent slab avalanches on steep north-facing aspects with 750 m wide crowns. A size 3.5-4 deep persistent slab avalanche was also observed. It is suspected this avalanche failed in depth hoar at the base of the snowpack.
See more on the potential of triggering deeper weak layers in our latest Forecasters' Blog.
Thursday's storm brings 20 cm of storm snow to the Pine Pass area and 10 cm elsewhere in the region. This adds to the 60 to 110 cm of recent storm snow over previously wind-affected surfaces. 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. 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.
Thursday Night
Partly cloudy with scattered flurries, 5 cm through most of the region. Up to 15 cm accumulation in the Pine Pass area. Ridge wind from the west 40-60 km/h. Alpine temperatures low to -3 C. Freezing level 1300 m.
Friday
Partly cloudy with isolated flurries, 5-10 cm accumulation. Alpine temperature high of -3 C. Ridge wind southwest 40 gusting 60 km/h. Freezing level 1200 m.
Saturday
Cloudy with sunny periods and isolated flurries, 1-5 cm accumulation. Alpine temperature high of -4 C. Ridge wind west 40-60 km/h. Freezing level 1000 m.
Sunday
Partly cloudy with isolated flurries, 5-10 cm accumulation. Alpine temperatures rise to -2 C. Ridge wind southwest 50-70 km/h. Freezing level 1500 m.
More details can be found in the Mountain Weather Forecast.
