Warming alpine temperatures may give some surprising releases, especially in steep terrain.
Confidence
Moderate - Timing or intensity of solar radiation is uncertain
Weather Forecast
Wednesday: Cold air in the valleys, warmer air up high that is expected to get close to 0C above 2200m. Some valley cloud is possible, clear at upper elevations. Light variable winds.Thursday: Clear in the morning, cloud developing through the day. Inversion conditions expected to persist. Moderate southwesterly winds.Friday: Cloudy with some flurries. Freezing level creeping up to around 1000 m. Some warm air remaining at higher elevations. Moderate southwesterly winds
Avalanche Summary
On Sunday, a size 1.5 avalanche involving two people near Invermere was reported. It was suspected to have run on the mid-December weak layer. On Saturday a skier triggered size 2 persistent slab avalanche running on a layer of facetted snow from mid-December was reported. This happened in the north of the region's Dogtooth Range on a west aspect at 2400m. Expect the potential to trigger persistent slabs to increase as last week's storm snow continues to settle into a cohesive slab.
Snowpack Summary
20-40 cm low density new snow has accumulated and buried a recently formed layer of weak feathery surface hoar and/or sugary facets. Another layer buried mid-December that consists of surface hoar, sun crust and/or sugary facets is down approximately 40-70cm and has been reported at elevations up to 2400 m. The likelihood of triggering avalanches on either of these layers is related to how dense the upper snowpack is. In areas where the upper snowpack has settled into a firmer slab, the weak layers below are more likely to be triggered. A rain crust that formed in late November is now buried 70-110cm deep. Recent reports show this layer to be unreactive at this time.
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.