If heavy snowfall arrives during the day on Sunday, consider alpine terrain to be at High danger.
Confidence
Fair - Intensity of incoming weather is uncertain
Weather Forecast
Sunday: There will likely be some heavy snow showers during the day before a more organized band of heavy snow arrives in the afternoon/evening. Amounts of 20-30 cm are expected by Monday morning. Freezing levels should stay around 400 m with strong southerly winds during the day on Sunday. On Monday, unstable air will bring another 10-15 cm new snow. On Tuesday, another intense Pacific frontal system arrives, which could bring as much as 40 cm new snow. Freezing levels may go up to around 1500 m. Continued strong westerly/southwesterly winds.
Avalanche Summary
Several small (size 1) skier-triggered slab avalanches were reported in exposed lee terrain (wind slabs) and in a band between 1700 and 1800 m (storm slabs) on steep terrain on a variety of aspects. Explosives were able to trigger slabs to size 2 in the most recent storm snow. Avalanches did not appear to be stepping down to lower layers.
Snowpack Summary
A cohesive slab has formed on the snow surface in response to new snow amounts that varied between 20-40 cm. The underlying snow was cold and in places, a layer of low density snow has been preserved. Reports indicate it may be particularly reactive between 1700 and 1800 m, although I would be concerned about this interface on all steep terrain right now. A rain crust lies buried approximately 30-50 cm below the snow surface at lower elevations (up to around 1800 m). Reports indicate the bond at this interface is quite good, although the slick nature of the crust may still provide a sliding layer in some steeper locations. Previous concerns about deeper weak layers appear to have now diminished. Snowpack depths at treeline are in the region of 260 cm.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.
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.