Snow, wind, and rising freezing levels will increase the avalanche danger. Deeply buried persistent weak layers may be triggered by the increased load from the storm. Patience and a conservative approach to terrain are recommended.
Summary
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Expect 5-10 cm of new snow overnight combined with moderate southwest winds and freezing levels around 200 metres. 10-15 cm during the day on Thursday with strong southwest winds and freezing levels around 500 metres. Extreme winds on Friday with heavy precipitation and freezing levels climbing up to about 1200 metres .Light to moderate precipitation on Saturday with moderate southwest winds and freezing levels dropping down to around 500 metres.
Avalanche Summary
One natural cornice release size 2.0 was reported from the north of the region on Tuesday. Reports from Monday include more evidence of natural avalanche activity that occurred during or post storm late last week with observations of recent widespread persistent slab avalanches up to Size 3.5. On Saturday, there was a report of a remotely-triggered size 2.5 avalanche that likely failed on the January 9th surface hoar. This slide occurred on South aspect at around 1200 m. Explosives control work in Ningunsaw Pass also produced numerous slab avalanches to size 3. Most of these slides were from N-E aspects in the alpine and at treeline. Many initiated on the mid-January surface hoar but then stepped down to deeper persistent weaknesses. This type of avalanche activity highlights the current challenge of dealing with buried persistent weak layers that are becoming harder to trigger, but if triggered they will produce very large and potentially deadly avalanches.
Snowpack Summary
Moderate winds on Wednesday may have started to build new wind slabs. There is 15-30 cm of lower density new snow that overlies moist or wet snow, or previously wind affected surfaces in the alpine. Over the past few days the wind has been minimal in most places but pockets of fresh wind slab could be found in lee and cross-loaded features in the alpine and at treeline. Sheltered alpine areas could be harboring a weak layer of surface hoar buried late last week, which was recently found down 60cm. The January 9th surface hoar/facet layer is down 70-150 cm in most places, and remains a concern on all aspects and elevations, especially with heavy and/or thin-spot triggers. Around the same depth you may also find a surface hoar/facet interface from around New Years. In the wake of the recent storm, there is a lot of uncertainty regarding the reactivity and distribution of this destructive persistent avalanche problem. A conservative approach to mountain travel is still required.
triley,
Avalanche Canada
