Watch for signs of instability as warm temperatures arrive in advance of Monday night's storm.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Tuesday
Weather Forecast
Monday: Periods of snow bringing 10-20 cm of new snow beginning late in the day. Winds moderate from the south. Freezing level to 1100 metres with alpine temperatures of -5.Tuesday: 15-20 cm of new snow accumulating. Winds moderate from the south. Freezing level rising to 1500 metres with alpine temperatures of -2.Wednesday: 10-20 cm of new snow accumulating. Winds moderate to strong from the south. Freezing level around 1600 metres with alpine temperatures around -1.
Avalanche Summary
Reports from Saturday show a decline in natural wind slab avalanches with small, skier triggered wind slab avalanches still occurring. Friday's reports included both natural and ski cut Size 1-1.5 wind slabs releasing from steeper convex features in north to northeast-facing terrain at treeline and above. Pockets of wind slab will likely remain reactive in immediate lee terrain over the short term. In shallow areas like Clemina Creek, it could be possible to trigger a layer of facets buried around 60 cm below the surface. Aside from these wind slab and possible persistent slab problems, additional caution is advised in steep terrain where loose snow sluffing may present an unexpected hazard.
Snowpack Summary
Cold and clear weather has promoted both faceting of surface snow as well as the growth of surface hoar that has been reported to be up to 10mm in size in protected areas. Below this surface, our recent new snow was shifted first by southwesterly winds and then by northerly winds. As a result, wind slabs exist on a variety of aspects at upper elevations. These accumulations have covered old, thicker wind slabs from previous wind events. A layer of faceted "sugar snow" and spotty surface hoar which formed during December's cold snap now lies roughly 1 metre below the surface. This layer is now dormant in many areas, but may still be a concern in shallow snowpack parts of the region, particularly around Clemina Creek. I'd continue to investigate this layer before committing to any large, unsupported features. The lower snowpack seems to be generally strong and well settled.
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.