Conditions are primed for widespread avalanche activity. Conservative decision making is essential for safe backcountry travel at this time.
Weather Forecast
Tonight and Wednesday: Moderate snowfall with 10-15cm likely overnight, and an additional 5cm on Wednesday. The freezing level (FL) drops overnight to 500-700m. Strong westerly winds overnight shifting to moderate-strong from the northwest on Wednesday afternoon. Thursday: Mainly dry under a weak ridge of high pressure. FL near valley bottom. Friday: Light snowfall - around 5cm. FL at valley bottom. Winds should be moderate from the southwest.
Avalanche Summary
There are several reports of natural and skier triggered avalanches up to Size 1.5. These avalanches occurred in wind affected terrain in the alpine, or on steep convex shaped features below treeline. The size and likelihood of avalanches will increase as the new snow settles into a more cohesive slab.
Snowpack Summary
Wind slabs continue to grow in exposed terrain in response to moderate W-SW winds. 20-50cm of slowly settling storm snow overlies the Feb. 9 weakness, which includes surface hoar and/or a crust. This surface hoar layer may be widespread in some areas, while others have reported it being confined to shady aspects at treeline and in the alpine. A melt-freeze crust has developed on solar aspects at all elevations, and on all aspects below about 1600 metres. The mid-pack is generally well settled. There is some concern that large loads like cornices may trigger the Jan. 20th facet layer. Some shallow snowpack areas may continue to have a weak layer of basal facets near the ground.
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.