Avoid slopes that have corniced ridgelines. Cornice failure may trigger large, persistent slab avalanches on the slope below.
Where a supportive crust exists, avalanches are unlikely.
Facets and/or surface hoar buried 40 to 80 cm deep are most prominent on north-facing slopes in the alpine. Avoid areas with a thin or variable (thin to thick) snowpack.
Cornice fall (large trigger) could be enough to trigger these slabs.
Watch for surface snow becoming moist, especially on solar slopes, with warm temperatures and sun.
On Monday, a 2.5 persistent slab avalanche was seen at Hudson Bay Mountain on an alpine (northeast) slope. It likely failed on Sunday from a cornice fall.
Higher north-facing slopes are still suspect for triggering persistent slabs, especially with a large load or in a thin to thick snowpack area. Where a thick, supportive surface crust is found, we expect that triggering avalanches on buried weak layers is unlikely.
Wind has modified surfaces and formed slabs in lee features. A crust is found up to 1500 m on all aspects and higher on solar slopes.
A layer of surface hoar is now buried 30 to 60 cm deep, it persists at alpine elevations and on 'polar aspects' (slopes protected from the sun).
Another layer of facets, surface hoar and/or a crust buried in mid-February is 60 to 100 cm below the snow surface and has been reactive in snowpack tests.
Deeper in the snowpack, a weak layer of facets and a crust from early December can be found. This layer appears to be dormant but is still worth keeping in mind in thin snowpack areas in the alpine.
Monday Night
Mix of clear and cloud. 10 to 25 km/h west ridgetop wind. Treeline temperature -3 °C. Freezing level valley bottom.
Tuesday
Mix of sun and cloud with isolated flurries. 15 to 30 km/h northwest ridgetop wind. Treeline temperature -5 °C. Freezing level 1000 m.
Wednesday
Mix of sun and cloud. 15 to 30 km/h northwest ridgetop wind. Treeline temperature -4 °C. Freezing level 1200 m.
Thursday
Mix of sun and cloud. 10 to 25 km/h west ridgetop wind. Treeline temperature -3 °C. Freezing level 1700 m.
More details can be found in the Mountain Weather Forecast.
