Avalanche Forecast
Issued: Feb 24th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs.
ahanna,
Avalanche Canada
"Not your typical North Shore storm slab," the current avalanche problem involves a weak layer sitting beneath 30-40 cm of recent snow. This problem is expected to persist longer than is usual for the region and requires extra precautions to avoid getting caught off guard.
Summary
Confidence
Weather Forecast
Monday night: Cloudy. Light to moderate northwest wind. Freezing level 700 m.
Tuesday: Around 5 cm new snow. Moderate west wind. Freezing level 800 m.
Wednesday: Cloudy. Light to moderate northwest wind. Freezing level 1000 m.
Thursday: Cloudy. Light to moderate southwest wind. Freezing level 1100 m.
Avalanche Summary
Explosive control work produced size 1-1.5 storm slabs running on a crust. Skier control work produced minimal results with limited propagation.
Snowpack Summary
30-60 cm of recent snow sits over a widespread layer of surface hoar which may sit on a breakable crust on solar aspects. Surface hoar is an exceptionally weak layer not often seen in this region, and the crust makes an excellent bed surface for avalanches. The recent snow which fell fluffy and light and lacking slab property, is settling into a slab with the aid of mild temperatures and strong winds.
As an analogy, think of a mattress (slab) resting on standing dominoes (surface hoar) on top of a glass table (crust). Imagine this configuration on a slope. It would not need to be prodded too hard to start sliding.
The remainder of the snowpack is well settled. Depth varies from around 250 to 300 cm at the peaks of the North Shore mountains (1400 m) tapering rapidly with elevation to no snow below 1000 m.
Terrain and Travel
- Avoid terrain traps such as gullies and cliffs where the consequence of any avalanche could be serious.
- Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.
- Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
- Any steep opening in the trees should be treated as suspect right now.
- Keep in mind that human triggering potential persists as natural avalanching tapers off.
Problems
Storm Slabs
30-60 cm of recent snow is settling into a storm slab over a weak interface consisting of surface facets, surface hoar or sun crusts (aspect/elevation dependent). This is not typical of this region and will take longer than usual to heal. The most problematic interfaces will be found in open areas around treeline sheltered from the wind with a clear sky view. A local ski area forecaster shared this advice on Sunday.
Storm slabs will be deepest where strong winds have loaded lee terrain features in alpine and exposed treeline areas. Recent wind has varied in direction from south to northwest, so expect to see wind loading on a variety of lee aspects.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 25th, 2020 5:00PM
