Fresh wind slabs are forming at higher elevations, and have the potential to step down to a lingering persistent weak layer. Watch for signs of instability and choose conservative routes.
Confidence
Moderate - Wind speed and direction is uncertain
Weather Forecast
SUNDAY: Morning flurries easing off in the afternoon, moderate northeast winds, alpine temperatures around -18.MONDAY: Mix of sun and cloud, light east winds, alpine temperatures around -22.TUESDAY: Sunny with cloudy periods, light east winds, alpine temperatures around -18.
Avalanche Summary
On Friday, there were numerous reports of size 2 avalanches including natural and skier-triggered loose dry avalanches and explosive-triggered wind slabs. There were also isolated reports of size 2 storm slabs on Saturday, including one that stepped down to glacial ice on a steep south-facing slope. Expect touchy wind slabs to develop as moderate winds redistribute loose snow in exposed terrain.Also, a notable MIN report from Friday shows what seems to be a size 2 persistent slab that was triggered by a ski cut in a cutblock west of Kimberly (see MIN report from Mallandaine Pass). This is a reminder that although avalanche activity on persistent facet layers has been intermittent, the problem will likely linger for some time in shallow snowpack areas.
Snowpack Summary
The region received a total of 40-60 cm of low density snow over the past week. Recent winds have come from a variety of directions and have loaded leeward and cross loaded features in exposed terrain. An interface that formed during the early December cold snap can be found buried 40-80 cm deep. The interface may consist of stiff wind-affected snow, faceted (sugary) crystals, or surface hoar crystals. The overlying slab appears to have a poor bond to the interface in some areas, such as wind-affected terrain in the Dogtooth range and shallow snowpack areas like the southern Purcells. The thick mid-November crust and facet layer is now buried 70-150 cm deep and appears to be dormant.
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.