Wind slabs may be rider triggered and could be surprisingly large.
Confidence
Moderate - Intensity of incoming weather systems is uncertain
Weather Forecast
Light flurries are forecast for the next few days of day of the forecast period, ending late Sunday afternoon. Strong southwest ridge top winds should become light to moderate by Sunday afternoon. Freezing levels will drop to valley bottom Sunday night, then rise again to1200m on Monday during the day.
Avalanche Summary
In recent days, several natural wind slab avalanches to size 1.5 were observed in high elevation terrain in the Elk Valley North area, as well as east of the divide. A size 1 persistent slab avalanche was also noted on a steep cut bank below treeline. Although observations were limited at the time of publishing this bulletin, strong winds on Thursday and Friday will likely produce a new round of wind slab activity. In areas where buried persistent weak layers exist, wind-deposited snow will also add to the likelihood and consequences of triggering the overlying slab.
Snowpack Summary
Recent snows form earlier in the week with strong southwest winds have been redistributed into wind slabs in higher elevation lee terrain. East of Crowsnest Pass new snow will overlie mainly scoured surfaces or hard stubborn wind slabs from last week. In general, the mid and lower snowpack are strong and well-settled in these areas.In areas to the west of the divide you're likely to find a mix of persistent weak crystals around 30cm below the surface. These crystals, which formed at the beginning of January, seem most reactive in open areas below treeline and consist of surface hoar, facets and a hard crust that formed on steep solar aspects. Additional snow load will add to the size and reactivity of this developing persistent slab. About 50cm below the surface you may also find a surface hoar layer which formed in December. Although no avalanches have been reported on this layer, it continues to produce sudden planar results in snowpack tests and may come to life with a large trigger or additional storm loading.
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.