Avalanche Forecast
Issued: Feb 9th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Wind Slabs.
cgarritty,
Avalanche Canada
Recent MIN reports from the region tell the tale of a widespread and tricky persistent slab problem. Cold temperatures are adding another layer of consequence to triggering it.
Summary
Confidence
Weather Forecast
Tuesday night: Increasing cloud with isolated flurries and a trace of new snow. Light to moderate west winds.
Wednesday: Becoming mainly sunny. Light northwest winds. Alpine high temperatures around -20.
Thursday: Sunny. Light northeast winds. Alpine high temperatures around -24.
Friday: Mainly sunny. Light northeast winds. Alpine high temperatures around -20.
Avalanche Summary
We are still receiving reports of persistent slab avalanches, triggered by skiers and explosives, generally large (size 2-3) with wide propagation, at elevations around treeline (1800-2000 m) where the persistent layer exists as surface hoar. Check out this great MIN describing a remotely triggered persistent slab avalanche in Kootenay Pass on Sunday. Most other MINs from the region from the past few days detail other persistent slab releases.
An explosives-triggered persistent slab in the Bonningtons on Tuesday stepped down to our early December crust layer to produce a 200 cm-deep, size 3.5 (very large!) avalanche.
A natural storm slab cycle up to size 2 was observed Saturday. Explosive and skier controlled storm slabs to size 1.5 were produced through the weekend.
Last week, an isolated size 3.5 (very large) avalanche was reported to have failed on a crust that was buried in early December. A smaller avalanche stepped down to this deeper layer, resulting in a very large and destructive avalanche.
Snowpack Summary
Snow from the past week has seen some wind effect at upper elevations and may contain a freezing rain crust or surface hoar at lower elevations. It continues to settle over a reactive weak layer buried 60-80 cm deep.
This persistent weak layer may exist as facets or a crust but it has been most reactive where it exists as large surface hoar crystals in sheltered areas treeline and below. Surface hoar has potential to surprise backcountry users with how widely the fracture can travel across slopes. This layer is slow to gain strength and requires careful terrain selection.
There are potentially several more layers of surface hoar in the upper snowpack, with the most notable one down about 80-120 cm. This layer was buried in early January.
A crust surrounded by weak faceted grains is buried deep within the snowpack. It may be possible to trigger this layers with a large load.
Terrain and Travel
- Be careful as you transition into wind affected terrain.
- Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.
- Be aware of the potential for large avalanches due to the presence of buried surface hoar.
Problems
Persistent Slabs
60-80 cm of snow sits on a persistent weak layer that was buried near the end of January. This layer has been the most reactive at treeline, where it exists as surface hoar.
Another layer of surface hoar that was buried in mid-January may still be possible to trigger, and it is now down about 80-100 cm.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Wind Slabs
Recent wind from southwest to northwest has blown recent snow into wind slabs in lee features at upper elevations.
In wind sheltered areas, low density storm snow may be prone to sluffing especially with skier traffic.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Feb 10th, 2021 4:00PM
