Watch out for lingering pockets of wind slab at treeline and in the alpine.
Confidence
High - Due to the number and quality of field observations
Weather Forecast
WEDNESDAY: partly cloudy, light southwesterly winds, 1500m freezing level with an inversion and above freezing level extending into the alpine. THURSDAY: mainly sunny, light southwest winds, freezing level rising to 2500m. FRIDAY: light snow through the day, light south winds, freezing level 2000m.
Avalanche Summary
Numerous natural and artificially triggered storm slab avalanches were reported over the last couple of days. Although natural avalanche activity is now slowing, wind slab avalanches are expected to remain reactive to human-triggering. Cornices are reported to be large and fragile, and may fail under the weight of a person.
Snowpack Summary
The recent storm snow continues to settle and gain strength, however, some lingering mid storm instabilities are still reactive to ski cutting in steeper terrain features. Ongoing southeast through southwest winds have been loading lee features in the alpine and at treeline and cornices are large and fragile. A thin breakable crust may cap moist snow on slopes that see direct sun. Several crusts can be found in the upper meter depending on elevation and aspect. The upper snow pack is sitting on a more widespread and thicker crust that extends into the alpine. In most places this crust is bridging a layer of surface hoar buried in early January. It is becoming increasingly hard to make this layer fail in snowpack tests and triggering an avalanche on it is unlikely.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.