Avalanche Forecast

Moderate - Intensity of incoming weather systems is uncertain on Friday

WEDNESDAY: Period of snow bringing 5-10cm of accumulation with freezing level near valley bottom and moderate southeasterly winds. THURSDAY: Light snow in the morning but increasing throughout the day with another 5-10cm expected by nightfall. Freezing levels around 800m and moderate to strong southerly winds. FRIDAY: Moderate to heavy precipitation and warm temperatures overnight Thursday and all day Friday concentrated primarily in the southern part of the region with up to 40mm of water equivalent and freezing levels as high as 1400m.

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.

15-30 cm of lower density new snow overlies moist or wet snow, or previously wind affected surfaces in the alpine. Recent 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.