Regions
Northwest Inland.
The storm this weekend is currently expected to only bring light amounts. Danger is still expected to rise on account of strong winds and rapidly rising temperatures.
Confidence
Moderate - Intensity of incoming weather systems is uncertain on Saturday
Weather Forecast
Friday: Flurries. Ridgetop winds increasing to around 70 km/h from the southwest. Temperatures rising from around -20C in the morning to -10C in the afternoon. Friday night: Up to 5 cm new snow with continued strong winds and rising temperatures.Saturday: a further 5 cm new snow expected, ridgetop winds around 70 km/h from the southwest and treeline temperatures touching 0C. Freezing level expected to be around 1200 m.Sunday: A break in the storm with flurries, winds around 40 km/h from the southwest, freezing level around 1200 m.
Avalanche Summary
On Tuesday, a skier accidentally triggered a size 2 wind slab on a 34 degree southwest facing slope at treeline. This avalanche occurred a few kilometres east of the Kispiox river valley. A natural avalanche also ran about that time near Ningunsaw. It was reported as a size 2.5 running on basal facets on a southwest aspect at 1700 m.
Snowpack Summary
Recent wind transport has shifted low density snow into wind slabs at upper elevations. Recently temperatures have been warmer in the alpine than in the valley, which may have made the alpine snow slightly firmer (in sheltered locations - it's already firm where it's been drifted by wind). Snow depth at treeline varies from about 1 m in most areas to 2 m in deeper snowpack areas in the south and west of the region. The shallow snowpack areas mostly consist of weak facetted or sugary grains beneath hard slabs. These hard slabs may produce surprisingly long fractures resulting in large avalanches, and in some instances they may step down to weak faceted snow crystals near or at the ground. In addition to the facets, a thick layer of buried surface hoar may be found 30-40 cm below the surface. There is another persistent weakness that formed during the early December cold snap which is now about 50-70 cm deep.
Problems
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.