Danger could be slightly higher in the alpine on Wednesday if we see snow accumulations of 10 cm or more with the approaching system.
Confidence
Fair - Intensity of incoming weather is uncertain
Weather Forecast
Tuesday: A frontal system approaches the coast and moves across the province. Flurries are expected during the day (2-3 cm) and moderate snow in the evening and overnight (~5 cm). Winds increase to strong from the southwest later in the afternoon. The freezing level is around 1200 m. Wednesday: Possible flurries early then a mix of sun and cloud. The freezing level drops to 500 m. Winds are light from the northwest. Thursday: A mix of sun and cloud. The freezing level is near valley bottom. Winds are light from the west.
Avalanche Summary
A couple new size 2.5 slab avalanches were triggered by explosive controlled cornice failures. The cornices triggered slabs on a steep north aspects that were 35-70 cm deep. Other than that, avalanche activity was limited to small loose sluffing in steep sun-exposed terrain.
Snowpack Summary
The snow surface consists of new wind slab in exposed alpine terrain, a sun crust on solar aspects, and surface hoar and/or facets on shady slopes. The recent storm slab continues to settle over old interfaces comprising of surface hoar, crusts and facets down 30-50 cm. However, areas that have buried surface hoar seem to be most touchy. Continued freezing temperatures overnight have helped to strengthen the snowpack at lower elevations.The mid-pack is generally well settled and the average snowpack depth at treeline elevations is near 130. Cornices have grown and may threaten slopes below.
Problems
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.