The persistent slab problem is shifting into a low-probability/ high-consequence situation. Be confident in your local snowpack before committing to any big terrain.
Confidence
Fair - Timing or intensity of solar radiation is uncertain on Sunday
Weather Forecast
Light snow fall (5-15 cm) is expected on Saturday and Sunday, petering to flurries on Monday, with a chance of sun. The freezing level is around 1500 m by day, falling towards valley floor by night. Winds are generally light.
Avalanche Summary
A skier was partially buried in a size 2.5 wind slab on a north aspect at 2600 m on Thursday. Some naturally-triggered wind slabs and cornice falls were also reported. 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.
Snowpack Summary
10-20 cm recent 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. Persistent weak layers in the upper snowpack remain a concern. The mid-March crust/facet layer is down around 60 cm. Down around 80 cm is the mid-February crust/facet/surface hoar layer. Both of these layers are slowly improving in strength, although it may still be possible to trigger one of these, causing a very large avalanche.
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.