Avalanche Forecast
Issued: Jan 28th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
astclair,
Avalanche Canada
Incoming snow and wind are expected to build increasingly reactive storm slabs and raise concern for a buried weak layer. Anticipate changing conditions and back off terrain as snow accumulates.
Summary
Confidence
Weather Forecast
Tuesday night: Cloudy, 5-10 cm of snow, strong southwest winds with extreme gusts, alpine high temperature -4 C.
Wednesday: Cloudy, 5-15 cm of snow, strong southwest winds, alpine high temperature -2 C, freezing level rising to 1000 m.
Thursday: Cloudy, 5-15 cm of snow, strong southwest winds, alpine high temperature -2 C, freezing level around 1000 m.
Friday: Cloudy, 5-10 cm of snow, moderate southwest winds with strong gusts, alpine high temperature -3 C, freezing level around 500 m.
Avalanche Summary
Several natural and human-triggered wind slab avalanches were reported over the weekend (up to size 2.5). Over the past week, there have been reports of storm slabs (up to size 2) releasing on a faceted interface from mid-January (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.
Snowpack Summary
Incoming snow and strong winds are expected to 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.
Terrain and Travel
- Storm slab size and sensitivity to triggering will likely increase through the day.
- Choose conservative terrain and watch for clues of instability.
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
Problems
Storm Slabs
Up to 20 cm of snow is forecast to accumulate by late afternoon on Wednesday, with the potential to form widespread storm slabs reactive to human triggering. Expect these slabs to develop sooner and to be more pronounced in areas where strong winds are drifting the snow into deeper, stiffer, and more touchy slabs.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
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.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Jan 29th, 2020 5:00PM
