Avalanche Forecast
Regions: Banff, Banff Yoho Kootenay, East Side 93N, Field, Kootenay, LLSA, Lake Louise, Sunshine, West Side 93N.
While cooling is expected to end the widespread natural avalanche cycle on Monday, the likelihood of human-triggering the persistent slab this week remains less certain.
Caution is still advised on slopes that do not exhibit a surface crust, which can be expected to be largely unaffected by last week's heating.
Confidence
Moderate
Avalanche Summary
This weekend, widespread slab avalanches were observed on steep, solar-exposed terrain entraining wet snow at lower elevations to sz 3. Several cornice failures were also reported at local ski resorts, triggering persistent slabs up to size 2.5.
Avalanche Control:
Saturday - Mount Whymper - 12 shots = 12 slabs sz 2.5-3.5 on the Jan 30 layer
Sunday - Simpson and Wardle - 13 shots = 14 slabs sz 1.5-3 mainly persistent slabs however a few stepped down into midpack or basal layers
Snowpack Summary
10 to 30 cm of snow fell last week on a weak layer of facets, surface hoar, or sun crust. Extreme west winds and warm temperatures have encouraged slab formation (and created solar crusts). Previous slabs, another 10 to 30cm thick sit on a similar weak layer (Jan 30).
The midpack is weak and faceted everywhere while depth hoar and crusts form an even weaker base in eastern areas where snow depths remain low. In these areas, the basal weaknesses should be carefully considered.
Weather Summary
A weak low moved into Alberta Sunday evening. Light NE winds will bring upslope snowfall and cooling.
A few cm of snow is expected overnight in eastern areas, with another 5cm reaching areas further west Monday as the low is pushed by a ridge forming behind it in Alberta. Up to 10cm is expected in total before winds shift back west Tuesday bringing clearing
Terrain and Travel Advice
- Keep in mind that human triggering may persist as natural avalanches taper off.
- A hard crust on the snow surface will help strengthen the snowpack, but may cause tough travel conditions.
Avalanche Problems
Persistent Slabs
Warm temps and extreme west winds have developed slab properties in the 10-30cm of recent snow that buries previous slabs. Together, these slabs are up to 60cm thick and have been reactive on two weak layers of facets, surface hoar, or sun crust. Human triggering will remain likely on polar slopes.
Aspects: North, North East, East, South East, West, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible - Likely
Expected Size: 1.5 - 3
Deep Persistent Slabs
Last week's storm added load to the shallow and weak snowpack seen in many areas of the region this season and there were a few avalanches involving the entire snowpack as this problem woke back up. We expect this problem will become dormant again as the snowpack settles and cools Monday.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Unlikely
Expected Size: 1.5 - 3