Avalanche Forecast
Regions: North Rockies.
An unevenly distributed surface hoar layer in the upper snowpack could catch you out. It's deep enough to cause problems. Factor this into your decision making by choosing smaller terrain features unless you are certain it does not exist in your area.
Confidence
Moderate - Uncertainties in both the snowpack structure and the weather forecast limit our confidence.
Weather Forecast
Friday night: Around 10 cm new snow with strong westerly winds.
Saturday: Mostly dry. Treeline temperatures around -6C. Strong southwesterly winds.
Sunday: Dry. Sunny in the morning but clouding over later on. Treeline temperatures around -5C. Moderate southeasterly winds.
Monday: 2-5 cm new snow. Treeline temperatures around -6C. Light southwesterly winds.
Avalanche Summary
On Wednesday, several size 1.5-2 avalanches were reported from north-facing slopes up to 1 m deep, most likely on a layer of buried surface hoar in the upper snowpack.Â
On Monday, a size 2 slab avalanche was reported, this also released on a layer of surface hoar.
A few large cornice released have been noted from the last several days, however I suspect these will become less likely with cooling temperatures and less sunshine.
Snowpack Summary
One or more buried surface hoar layers are buried in the upper snowpack at depths of around 45-65 cm. Buried surface hoar has been confirmed in the Pine Pass, Torpy & Renshaw zones, it may be more widespread throughout the region too. It's now sufficiently deep to result in a large avalanche if triggered, so this layer should be factored into your decision-making process.
The mid-and lower snowpack layers are generally well-bonded, except for shallow and/or rocky start zones which could harbour weak basal snowpack layers.Â
Terrain and Travel
- Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
- Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
- Caution around slopes that are exposed to cornices overhead.
Avalanche Problems
Wind Slabs
New snow and strong winds will make avalanches likely on steep, wind-affected slopes, particularly on Friday and Saturday.
Aspects: North, North East, East, South East, South, North West.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 2.5
Persistent Slabs
A weak layer of surface hoar buried typically 45-65 cm below the surface has been reported from the following zones: Renshaw, Torpy and Pine Pass. It may exist elsewhere in the region. Treeline slopes such as this (here's the MIN post) are the most likely areas to harbour this problem.
Aspects: All aspects.
Elevations: Treeline.
Likelihood: Possible
Expected Size: 1.5 - 2.5