Recent deep persistent slab avalanche activity has highlighted the importance of thoughtful terrain selection in a region that harbours a fundamentally weak basal snowpack. Don't let yourself become complacent around big alpine features as wind slab problems fade out.
Wind slabs have formed above a widespread crust, natural activity has slowed down, but human triggering may remain possible on steep crossloaded or leeward features.
Our weak basal snowpack has produced sporadic very large avalanches - both natural and human triggered - in recent days. More details here and here. When considering terrain you need to be thinking about the potential for deep avalanches. The most likely trigger points are thin rocky areas near ridge crest. Rock outcroppings in exposed terrain should be avoided.
Wednesday night: Cloudy with possible clear periods. Light northwest winds, increasing into the morning.
Thursday: Becoming cloudy with light flurries beginning late afternoon. Moderate to strong southwest winds. Alpine high temperatures around -7 with freezing levels reaching 1400 metres.
Friday: A mix of sun and cloud with continuing isolated flurries and a trace of new snow, 5-10 cm including the overnight period. Moderate southwest winds, increasing a bit overnight. Alpine high temperatures around -8.
Saturday: Mainly cloudy with isolated flurries and a trace of new snow. Moderate to strong southwest winds. Alpine high temperatures around -7.
On Monday reported avalanche activity was limited to small dry loose avalanches and a single small wind slab that succumbed to explosive control work. No new avalanches were reported on Tuesday, however another recent large deep persistent slab is described in the following MIN report.
Over the weekend numerous natural, human triggered and control work induced avalanches to size 2 were observed, there is a great MIN that serves as an example of this kind of activity here.
There was also a bigger avalanche reported in this MIN on February 9th (check out the photos, they're humbling). The very large avalanche ran on a north facing feature at 2400 m and was triggered by a snowmobile. The group was using excellent travel protocol and thankfully no one was hurt. 10 or so climbs had been made in the same area in the days leading up to this avalanche without incident - a great illustration of the tricky, low probability/high consequence nature of persistent slabs.
Before the above avalanche, the last avalanche cycle to include persistent slabs was during the first weekend in February when some large (size 2.5) deep persistent slab avalanches in the Elk Valley (see photos in this MIN report) ran. These patterns of activity suggest our deep persistent slab problem may resurface more decisively during stormy periods but also that it can't easily be ruled out even when surface instabilities are limited.
5 to 15 cm of storm snow from last weekend's storm adds to the variable amounts of wind affected snow that sits above a widespread rain crust that exists up to roughly 2100 m. The storm snow has been formed into slabs by wind from a variety of directions.
The Elk Valley has about 5-20 cm of snow above the crust while the eastern slope of the region has closer to 15-35 cm above the crust. There have been observations of surface hoar forming in the Elk Valley previous to Friday Night's storm, check that out here. A well consolidated mid-pack overlies generally weak basal facets, that may be possible to trigger in isolated shallow rocky start zones.
