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: Flurries bringing 10-15cm of new snow beginning late in the day. Winds moderate from the south. Freezing level rising to 1000 metres with alpine temperatures to -6 Tuesday: Flurries and periods of snow delivering 10-20 cm of new snow. Winds moderate from the south. Freezing level rising to 1400 metres with alpine temperatures of -3. Wednesday: Flurries and periods of snow delivering 10-15 cm of new snow. Winds moderate gusting to extreme from the south. Freezing level rising to 1700 metres with alpine temperatures around -1.
Avalanche Summary
No new avalanches were observed on Saturday. Friday's reports indicated Size 1-1.5 wind slab avalanches were continuing to run naturally in steep terrain, with the most recent activity observed on north aspects near Valemount. Aside from wind slab and persistent slab problems, additional caution is advised in steep terrain where loose snow sluffing may present an unexpected hazard.
Snowpack Summary
Recent 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 7mm in size in sheltered areas below treeline. Below the surface, our recent storm snow was redistributed by moderate to strong southwest and more recent northerly winds in exposed upper areas. In deeper snowpack parts of the region, the mid-December facet layer lies up to 120 cm below the surface. In these areas, professionals feel this layer has generally gained considerable strength. In shallower areas, particularly those in the southeast (Allen Creek), North (Sugarbowl) and likely some western areas around Quesnel and Barkerville, the snowpack is likely a lot more suspect, with a thicker, more pronounced facet layer buried only 50-60 cm below the surface. In shallow snowpack areas such as these, recent cold temperatures have had the effect of weakening the entire snowpack, not just its upper layers. A careful evaluation of this facet layer is strongly advised before to any push into steeper terrain in a shallow snowpack area.
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.