A week of snowfall and strong winds has left wind slabs and some cornices primed for human triggering. Avoid overhead hazards and evaluate terrain carefully before committing to bigger lines.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
We're looking at occasional (intense) flurries and cool temperatures throughout the forecast period. TUESDAY: Flurries with up to 5cm of new snow, 20-40 km/h southeast winds, alpine temperatures around -11 C. WEDNESDAY: Flurries with 5-10 cm of new snow, 20-30 km/h east winds, alpine temperatures around -12 C. THURSDAY: Cloudy with scattered flurries and up to 3-5 cm of new snow, 30-50 km/h east winds, alpine temperatures around -14 C.
Avalanche Summary
On Saturday, several size 2 natural storm slabs were reported in alpine terrain and explosive control and ski cutting produced size 1-1.5 avalanches at treeline and in the alpine.Natural activity is expected to taper off, but storm and wind slabs will remain susceptible to human triggering.
Snowpack Summary
We've had another 15-25 cm of snow since Saturday, bringing the total from the past week to 50-80 cm. Strong southwesterly winds redistributed the new snow onto leeward slopes, building thicker and stiffer slabs. The new snow will likely have a poor bond to the old snow interface that consists of stiff wind slabs, crusts, and facets. The mid-pack in this region is generally strong, but the bottom third of the snowpack is composed of weak facets (sugary snow crystals). Approximately 100-120 cm of settled snow sits above this weak layer of sugary, rotten facets that developed in December. This remains a concern and should be on your radar, especially with the recent loading from snow and wind.
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.
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.