Avalanche Forecast
Issued: Dec 24th, 2019 5:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs.
dsaly,
Avalanche Canada
Snowfall and wind continue to progressively load the snowpack, developing a slab over a weak surface hoar layer. Its hard to know when the load will be great enough to induce a natural avalanche cycle, for now a cautious approach to avalanche terrain is recommended.
Summary
Confidence
Moderate - Uncertainty is due to whether buried persistent weak layers become active, triggering avalanches, with the arrival of the forecast weather. Uncertainty is due to unpredictable avalanche behavior.
Weather Forecast
Tuesday Night: Cloudy with isolated flurries, trace to 5 cm. Alpine temperature -8 C. Southwest wind, 15-35 km/hr. Freezing level valley bottom.
Wednesday: Cloudy with isolated flurries, up to 5 cm. Alpine temperature -7 C. Southwest wind, 25-55 km/hr. Freezing level 100 m.
Thursday: Heavy snow, 30-55 cm. Alpine temperature -3 C. Southwest wind 25-30 km/hr gusting to 70 km/hr. Freezing level 800 m.
Friday: Snow and flurries, 15-25 cm. Alpine temperature -2 C. Southwest wind 30-40 km/hr gusting to 75 km/hr. Freezing level rising to 1100 m.
Avalanche Summary
Early Tuesday, avalanche control work north of Stewart triggered two size 2 storm slab avalanches, this area accumulated 25 cm new snow by Tuesday morning.
Last Thursday natural storm slab to size 2 avalanches were reported in the Shames area, following the snowfall. Further north in the region, explosives triggered storm slab avalanches to size 2. Surface hoar, which the storm snow fell on, was the likely weak layer involved. A MIN report here from Saturday identifies and discusses reactive surface hoar buried 70 cm under the recent storm snow.
Snowpack Summary
15-30 cm recent snow being impacted by south-southwest wind, at upper elevations windslabs have developed in lee features. In total, 40-70 cm recent snow overlies a weak layer of surface hoar, old faceted surfaces, and/or a crust on south/southwesterly alpine slopes.Â
The layer of surface hoar, down 40-70 cm is concerning as it continues to be reactive in snowpack tests providing evidence it is at a tipping point where any additional load (such as a person) could trigger an avalanche on this layer.Â
Reports from the Shames area suggest the surface hoar layer is on all aspects, but more prevalent on southeast to southwest aspects around 800-1400 m, and more likely on leeward and sheltered alpine areas.
The lower snowpack is generally considered strong, as there has been very little to report in terms of recent avalanche activity or snowpack test results on deeper layers. Snowpack depths at treeline range from 100-250 cm and taper quickly at lower elevations.
Terrain and Travel
- Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Problems
Persistent Slabs
50-80 cm snow is settling over a weak layer of surface hoar. Additional flurries and winds continue adding load and building slabs. It is uncertain when this layer may become reactive as the snow above gradually accumulates and consolidates. Certainly it is right at the tipping point, so making conservative terrain choices is the best way to manage this problem.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 25th, 2019 5:00PM
