Heavy snowfall and intense wind continues to add to a widespread and reactive storm slab problem. With more snow and wind on the way, seek out simple and sheltered terrain and avoid overhead avalanche hazard.
A layer of weak, faceted snow from the previous cold snap is now buried 70-140 cm deep. Snowfall and wind are adding a rapid load this persistent weak layer, potentially bringing it to its tipping point. Smaller storm slab avalanches have the potential to step-down to this layer resulting in very large, destructive avalanches.
Heavy snowfall with strong to extreme winds developed a widespread, reactive storm slab problem. Expect these slabs to be more pronounced in areas where strong winds are drifting the snow into deeper, stiffer, and more touchy slabs.
Thursday night: Snow, 10-25 cm. Alpine low temperature -5 C. Strong gusting to extreme southwest wind. Freezing level 500 m.
Friday: Flurries and snow, 10-20 cm. Alpine high temperature -5 C. Moderate southwest wind gusting strong to extreme. Freezing level 500 m.
Saturday: Flurries and snow, 5-15 cm. Alpine high temperature -7 C. Moderate southwest wind gusting to strong. Freezing level 200 m.
Sunday: Mix of sun, cloud, and isolated flurries. Alpine high temperature -10 C. Light southwest wind occasionally gusting to strong. Freezing to sea level.
On Wednesday, small (size 1-1.5) storm slabs were triggered by explosives further north in the region. A few larger (up to size 2.5) slab avalanches observed Wednesday morning, they likely failed naturally overnight due to a combination of new snow and strong wind. As more snow accumulates with strong winds, storm slabs are expected to grow in size and reactivity.
Last Sunday, small pockets of human-triggered wind slab were recently reported at treeline elevations closer to Terrace, while larger (size 2-3.5) wind slabs were reported further north in the Bear Pass area releasing naturally from alpine start zones. Several of these avalanches released down to a weak layer formed in mid-January. During the weekend warm-up, numerous natural loose wet avalanches in steep terrain (size 1-2) were observed up to 1000 m.
Reports of deep persistent slab avalanches have been trickling in throughout the month, with a size 2.5 deep persistent avalanche triggered by explosives in the Ningunsaw area on Tuesday. Prior to this avalanche, the last reported event occurred on Jan 17th. They are associated with a November crust layer near the base of the snowpack which has produced very large avalanches (size 3+) with crown depths of around 2 m. These have typically run in alpine terrain, on lee or cross-loaded slopes. Recent loading has been a good test for this layer and it seems to be trending less reactive.
50-70 cm new snow through Thursday (and still counting) has been heavily impacted by strong southwesterly winds forming a reactive storm slab. This new snow overlies a variety of wind affected surfaces in exposed treeline and alpine areas.
Snowfall from the second half of January over lies a thin layer of facets, down 70-140 cm, that formed during the mid-January outflow event. Recent avalanche activity in the Bear Pass area and snowpack tests results have indicated that this layer is still a concern (check out this MIN report). Below tree line, a recent warm-up moistened snow surfaces up to 900 m, forming a temperature crust.
A crust from mid November lurks at the base of the snowpack. The last reported avalanche on this layer was Jan 17th. While it is promising that last week's significant snowfall did not trigger avalanches on this deep persistent weak layer, there is lingering uncertainty as to whether this week's weather could meet the threshold.
