The persistent slab problem is still on the radar, but shifting into a low-probability/ high-consequence situation. Be confident in your local snowpack before committing to any big terrain.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Light snow starts on Friday night and continues through the weekend. (Estimates: 5-10 cm on Saturday; 1-5 cm on Sunday). Light flurries continue on Monday. The freezing level is around 1600 m by day, falling towards valley floor by night. Winds are generally light.
Avalanche Summary
Persistent slab, storm slab, and loose wet avalanche activity has tapered off recently. While the likelihood of triggering a large avalanche has gone down, the consequences remain high. On Wednesday, a naturally-triggered size 2.5 wind slab was observed on a NE aspect at 2500 m. An ice fall also triggered a size 3 deep persistent slab which failed at ground. Human-triggered wind slabs and persistent slabs are still a concern, especially on steep, unsupported slopes in the alpine. Stability is generally expected to improve with the cooling trend but this may take a few days at higher elevations.
Snowpack Summary
10-20 cm dry convective snow was shifted by NW winds into wind slabs on lee slopes in the alpine. These overlie a recently formed crust which varies in thickness with elevation. Below about 2000 m, loose moist snow makes up much of the snowpack underneath a surface crust. Several persistent weak layers exist in the upper metre of the snowpack which remain a concern. The mid-March crust/facet layer is down around 60 cm and has been reactive to light triggers recently. Down around 80 cm is the mid-February crust/facet/surface hoar layer which has also been reactive to heavy loads like avalanches in motion stepping down, cornice failures, or explosives.
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.