A bit of new snow and sustained winds have kept our wind slab problem alive and well. In sheltered areas, new snow may be a thin mask over buried slabs.
Weather Forecast
Thursday night: 5-10cm of new snow with moderate to strong winds from the west.Friday: Mostly cloudy with isolated flurries and a trace of new snow. Winds light gusting to moderate from the west. Alpine temperatures ranging from -7 in the south to -14 further north.Saturday: Mainly cloudy with isolated flurries and a trace of new snow. Winds light gusting to moderate from the west. Alpine temperatures around -12.Sunday: A mix of sun and cloud with no new snow. Winds light from the northeast. Alpine temperatures ranging from -12 in the south to -19 in the north.
Avalanche Summary
Limited avalanche control took place in the northern part of the region on Wednesday and produced several size 1.5-2.5 avalanches. Crown depths ranged from 20-40cm. These occurred at high elevations and are attributed to wind slabs that have grown with recent wind and snow loading. An ACMG Mountain Conditions Report from Christmas day describes a slab avalanche failing on a steep, north facing slope at 2100m. This avalanche remains relevant for having stepped down 110cm to the November crust. The size of the avalanche is unknown, but this speaks to the touchy nature of persistent slabs in the area. On Christmas eve, a skier was partially buried in a size 2 slab avalanche while skinning up a northeast facing slope at about 2000m. The failure plane of this avalanche is unknown although the depth (40cm) suggests the mid-December weak layer may have been the culprit. Check out the Mountain Information Network post for more details.
Snowpack Summary
Between 15-20cm of new snow has fallen in the past few days. Moderate southwest winds have been redistributing the loose surface snow into new wind slabs in exposed higher elevation terrain. A highly variable 20-80 cm of snow overlies the mid-December interface which consists of stiff wind affected snow, faceted (sugary) crystals, and surface hoar that formed in sheltered areas. The overlying slab appears to have a poor bond to these surfaces in some areas, especially in wind-affected terrain in the Dogtooth range and possibly Quartz Creek. In sheltered terrain, the overlying slab has remained soft. As it continues to settle and gain cohesion, we may start to see a more widespread persistent slab problem develop. The thick mid-November crust/ facet layer typically sits 70-140 cm down in the snowpack. Recent avalanche activity in the Dogtooth Range suggests this layer has woken up and has the potential for large avalanches. Check out this ACMG Mountain Conditions Report for more info: https://mountainconditions.com/reports/december-25th-dogtooth-range-november-crust-awakening
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.