Extreme winds, intense snowfall, and fluctuating temperatures will create complicated and dangerous conditions. Hang on to your hat, keep your head on a swivel, and stick to simple terrain.
A layer of weak, faceted snow from the previous cold snap is now buried 70-140 cm deep. The incoming snowfall and wind will add a rapid load this persistent weak layer, potentially bringing it to its tipping point. Easier-to-trigger avalanches in the storm snow have the potential to step-down to this layer resulting in very large, destructive avalanches.
30-40 cm of snow is forecast to accumulate by late afternoon on Wednesday, forming 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.
Tuesday night: Cloudy, 15-25 cm of snow above 800 m, extreme south wind, alpine temperature -1 C, freezing level rising to 1000 m.
Wednesday: Cloudy, 10-20 cm of snow above 800 m, strong southwest winds, alpine high temperature -2 C, freezing level around 800 m.
Thursday: Mostly cloudy, 35-45 cm of snow above 800 m, strong south winds with extreme gusts, alpine high temperature -1 C, freezing level around 800 m.
Friday: Cloudy, 25-35 cm of snow above 500 m, strong south winds, alpine high temperature -2 C, freezing level around 600 m.
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 the last reported event occurring 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.
A powerful storm is impacting the region with intense snowfall, extreme winds, and fluctuating temperatures. Rapid snow accumulations are expected to build a touchy storm slab problem, particularly in wind-exposed areas. The intensity of the wind has the potential to reach areas well below treeline and form slabs in normally sheltered areas. Fluctuating freezing levels throughout the storm present an additional layer of complexity that may promote instability in the storm snow.
Last week's 50-120 cm of snow accumulation rests on a mix of previously scoured surfaces from the arctic outflow winds or a thick layer of weak facets. 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.
