Rapid warming in the alpine and a persistent weak layer 30-50 cm below the surface are both good reasons to be cautious.
Weather Forecast
Tuesday: Cold air in the valleys, warmer air up high. An above freezing layer is expected from approximately 2300-2700 m. Some valley cloud is possible, clear at upper elevations. Light southwesterly winds.Wednesday: basically a repeat of Tuesday, possibly slightly warmer.Thursday: Cloud developing later in the day. Lower elevations getting warmer, although the above freezing layer is expected to remain in place. Light 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. 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.