Snow and wind will build increasingly reactive storm slabs and stress a buried weak layer. Seek out simple and sheltered terrain as snow accumulates.
A layer of weak, faceted snow from the January cold snap is now buried 40-70 cm deep. The incoming snowfall and wind is expected to load this persistent weak layer, potentially bringing it to its tipping point.
Strong and gusty winds with new snow will build reactive storm slabs. Expect these slabs to develop sooner and be more pronounced in areas where strong winds are drifting the snow into deeper, stiffer, and more touchy slabs.
Wednesday night: Flurries, up to 10 cm. Alpine low temperature -10 C. Moderate southwest winds gusting to strong.
Thursday: Snow, 10-15 cm. Alpine high temperature -4 C. Strong gusting to extreme southwest winds. Freezing level rising to 1000 m.
Friday: Flurries and snow, 5-20 cm. Alpine high temperature -3 C. Moderate southwest winds gusting strong to extreme. Freezing level 1000 m.
Saturday: Flurries, 5-15 cm. Alpine high temperature -9 C. Moderate west wind gusting to strong. Freezing level dropping to valley bottom.
Several natural and human-triggered wind slab avalanches were reported last weekend (up to size 2.5). Reports indicate that recent storm and wind slab avalanches have failed on a faceted interface from mid-January that developed with cold temperature prior to the last heavy snowfall (see an example in this MIN report).
There have been reports trickling in over the past month of natural persistent slab avalanches up to size 3 in the Bulkley Valley. These are thought to have been failing on the November crust/facet layer near the ground. The last reported avalanches on this layer were Monday January 13th. Incremental snowfall and mild temperatures have likely promoted a decreasing trend in reactivity for this avalanche problem.
Incoming snow and strong winds will build a reactive storm slab problem, particularly in wind-exposed areas.
Below the new snow, last week's 25-40 cm of snow accumulation rests on mix of previously scoured surfaces from the arctic outflow winds or a weak layer of facets. The incoming snowfall and wind will add a new load this persistent weak layer, potentially bringing it to its tipping point.
A layer of surface hoar now buried up to 1 m below the surface may also be found at treeline. A deep crust/facet layer lurks at the base of the snowpack. A couple of large avalanches are suspected to have run on this interface earlier in January. These have typically run in alpine terrain, on lee and cross-loaded slopes. While it is promising that last week's 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.
