Large destructive avalanches remain possible in many types of terrain. Conservative route selection is recommended since it will be difficult to identify dangerous slopes.
Recent storm snow remains suspect at all elevations, especially in northern parts of the region where there has been more snowfall. It's settling above a variety of crust and surface hoar layers which makes it difficult to pinpoint where it will remain reactive. At upper elevations, wind will likely keep slabs reactive on leeward features, especially along ridges.
The early December crust can be found down 80-200 cm below the surface, with weak, sugary crystals (facets) on top of it. Large avalanches have been observed at all elevations and although the likelihood of triggering an avalanche is decreasing, there is ongoing concern for avalanches stepping down. We are now in a low probability/high consequence scenario with this layer.
TUESDAY NIGHT: Clear skies, light wind from the northwest, treeline temperatures around -10 C.
WEDNESDAY: Clear skies in the morning with increasing cloud in the afternoon, light wind from the southwest, treeline temperatures warming to -5 C.
THURSDAY: Moderate snowfall with 5-15 cm of new snow, strong wind from the southwest, treeline temperatures warming to -3 C with freezing level reaching 1000 m.
FRIDAY: Mostly sunny, light to moderate wind from the northwest, treeline temperatures around -2 C.
A notable natural avalanche cycle occurred on Monday. Numerous very large (size 3) avalanches were reported in the Selkirks east of Revelstoke (including neighbouring Glacier National Park). These layers occurred at all aspects and elevations and involved both storm slab and deep persistent slab avalanches. The remaining parts of the region did not experience the same level of widespread large avalanches, but there were still many size 1-2 storm slabs across the region and a few reports of large deep persistent slab avalanches in Central Kootenays and Monashees.
Most of the deep persistent slab avalanches occurred at below treeline elevations (1700 - 2000 m), with many of them triggered by smaller storm slab avalanches starting at higher elevations. These avalanches have typically been 100-150 cm deep and occurred on northeast to northwest aspects.
20-30 cm of recent snow has likely been redistributed into leeward terrain at upper elevations. The amount of new snow is greater in northern parts of the region (e.g. near Revelstoke) than southern parts (e.g. near Nelson).
The upper snowpack contains a complex mix of crusts and small surface hoar layers. We are uncertain about where the most reactive layers may exist, but have noticed the following trends:
While none of these may be obvious widespread weaknesses, the combination and complexity require careful travel in avalanche terrain.
The one widespread weak layer in the Columbias is a more deeply buried crust/facet layer that formed in early December. It is typically down 80-140 cm, but as deep as 200 cm in wind loaded terrain. There has been regular avalanche activity on this layer at all elevations for over a month, and we expect to see continued sporadic very large avalanches.
