Reactive deposits of snow will be touchiest where impacted by wind - use caution around ridges and loaded features. Investigate deeper layers in the snowpack before committing to terrain.
Earlier winds were south-southwesterly and will transition to more northerly, resulting in wind slabs on a variety of aspects and an inconsistent redistribution of snow.
Triggering large avalanches on weaknesses in the lower snowpack remains a possibility. In some areas the concern is weak snow around crusts 70-100 cm deep, while in others it is weak snow near the bottom of the snowpack. Human triggering of these layers are most likely in steep, rocky slopes with a shallow or thin to thick snowpack.
TUESDAY NIGHT - Clearing and cooling / northwest wind, 20-40 km/h / alpine low temperature near -9 / freezing level valley bottom
WEDNESDAY - Cloudy with sunny breaks / northeast wind, 10-20 km/h / alpine high temperature near -6 / freezing level valley bottom
THURSDAY - Mostly sunny / east-northeast wind, 10-20 km/h / alpine high temperature near -8 / freezing level valley bottom
FRIDAY - Sunny / northeast wind, 10-30 km/h / alpine high temperature near -10 / freezing level valley bottom
On Monday in the Ningunsaw area, explosives triggered an impressive size 4 persistent slab avalanche which took out mature forest, and another five size 2.5-3 persistent slab avalanches in adjacent terrain. Additionally, wind slabs were reactive to skier traffic and explosives triggered wind slab avalanches to size 2.
A handful of wind slab avalanches to size 2 failing naturally were observed Sunday. Avalanches to size 2 were reported on more southwesterly to southeasterly aspects above 1200 m. Skiers easily cut size 1 pockets in loaded terrain.
A natural avalanche cycle occurred Thursday into Friday with storm and wind slab avalanches to size 2, with poor visibility likely limiting alpine observations. The strong winds reached below treelline elevations - reports of numerous wind slab avalanches observed in steep terrain with crowns 20-30 cm deep and up to 150 m wide. Check out this MIN report here of a large persistent slab avalanche that likely occurred during the Thursday-Friday natural cycle.
Just over a week ago, explosives triggered a few size 2 persistent slab avalanches near the southern boundary of the region (Jan 10). And explosive control work near Ningunsaw (just outside the region, on Jan 9) produced several wind slabs to size 2.5 and one size 3 deep persistent slab failing on weak facets near the base of the snowpack. As we continue to track this persistent weak layer, these are a reminder of the "low probability; high consequence" scenario that persistent slab problems often create.
Another 5-15 cm fresh accumulating around the region Tuesday adds to the recent incremental snow. Gusty and variable winds have impacted loose snow and developed slabs in exposed areas. Warm temperatures have produced a crust up to 800 m and higher on solar aspects.
A layer of surface hoar maybe be found under recent storm snow (now down 20-50 cm) around treeline. In the south of the region, another weak layer of surface hoar that was buried around the New Year has been reported down 50-70 cm in sheltered areas.
The lower snowpack has two crusts with potentially weak, faceted snow around them. Reports from the Smithers area suggest the upper crust is 70-140 cm below the surface and has shown signs of being possible to trigger from shallow areas. The deeper crust is near the bottom of the snowpack and is most likely to trigger from steep, rocky slopes, with a shallow or thin to thick snowpack. Recent avalanches failing on this basal layer were reported from the Ningunsaw area.
