New wind slabs may form on Saturday as the winds increase and old wind slabs may still be lingering around ridge crests. In isolated areas, the weak layer from early December may still be reactive. Continually assess local conditions as you travel.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Mostly cloudy conditions are expected on Saturday as a storm system approaches the interior. Light intermittent snowfall is possible during the day with alpine winds increasing to moderate to strong from the SW. Treeline temperatures are expected to be around -15C during the day. The main part of the storm is expected to affect the region Saturday night and Sunday. 2-4cm of snowfall is expected for the snowy parts of the region. Alpine winds are expected to remain moderate to strong from the SW and treeline temperatures will climb to around -10C. Unsettled conditions are expected on Monday as the remnants of the storm are pushed out by a ridge of high pressure.
Avalanche Summary
On Wednesday, two skier accidental avalanches were reported in the Golden backcountry. The first occurred in the morning and was a size 2 wind slab avalanche which occurred on a northwest aspect at about 2400m. It was up to 50cm in depth and ran approximately 600m. The second occurred in the afternoon and was a size 2.5 wind slab at ridgetop. This also occurred on a NW aspect at 2400m elevation. This avalanche stepped down to a deeper layer lower down in the start zone, likely the early December interface. On Thursday, a large settlement was felt in a flat meadow in the Invermere backcountry. This occurred at 2200m in a below treeline terrain feature and the failure layer is unknown.
Snowpack Summary
Throughout last weekend there was up to 20cm of new snow. Strong southwesterly winds had redistributed much of this snow into wind slabs in exposed lee features in the alpine and at treeline. With the current cold weather, I'd suspect continued faceting in the snowpack. Areas most affected would include windward or cross-loaded rocky areas at higher elevations. New wind slabs are expected to form this weekend as winds increase with the approaching storm. Between 40 and 80cm below the surface you'll likely find a layer of weak buried surface hoar which is most prominent between 1400m and 1800m although it may extend to higher elevations in some parts of the region. A weak sun crust with small facets and/or surface hoar also exists at higher elevations. Snow pit tests suggest that human triggering of this interface is becoming unlikely, although a release at this interface could be destructive in nature.
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.