The current conditions require restraint and conservative decision-making. Triggering the weak layer is getting more difficult but large avalanches, even from relatively low-angle slopes, remain possible. New wind slabs may also form on Tuesday.
Confidence
Moderate - Intensity of incoming weather systems is uncertain
Weather Forecast
A weak storm pulse is expected to bring 5-10cm of new snowfall to the region on Tuesday. Freezing levels are expected to be around 1500m and alpine winds are forecast to be moderate to strong from the southwest. A mix of sun and cloud is expected for Wednesday with freezing levels reaching around 1500m and light to moderate southwest winds in the alpine. A more substantial storm front is expected to reach the region on Wednesday night or Thursday morning. 15-25cm of snowfall is currently being forecast with freezing levels around 1700m and strong southwest winds.
Avalanche Summary
Numerous slab avalanches up to size 3 were reported over the weekend. Most of the natural avalanche activity occurred on Friday and Saturday but several were still reported on Sunday. A large number of skier triggered avalanches were also reported. Many of these failed at treeline and below on buried surface hoar down 30-60 cm. Many of these were triggered remotely, highlighting the volatility of the persistent slab. An increasing number of wind slabs have also been failing at alpine/ treeline elevations, and also running on surface hoar. While the natural activity tapered off since Saturday, the persistent slab is expected to remain reactive to human triggering for several more days. New wind slabs may form on Tuesday with the progression of the weak storm system.
Snowpack Summary
Recent snowfall and strong winds have created some storm slabs but reactive wind slabs on features lee to the southerly winds seems to be the bigger concern in the upper snowpack. This has added additional load and stress to an already touchy persistent slab. This 40-90 cm thick persistent slab overlies a variety of surfaces including large surface hoar, sun crusts, rime crusts and facets. The slab is ripe for human and natural triggers and is especially touchy at and below treeline. The mid and lower snowpack are generally well settled and strong.
Problems
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.
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.