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. 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 100-200 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 -12 C.
WEDNESDAY: Clear skies in the morning with increasing cloud in the afternoon, light wind from the southwest, treeline temperatures warming to -6 C.
THURSDAY: Moderate snowfall with 10-20 cm of new snow, strong wind from the southwest, treeline temperatures warming to -4 C with freezing level reaching 1000 m.
FRIDAY: Mix of sun and cloud, moderate wind from the northwest, treeline temperatures around -4 C.
A notable natural avalanche cycle occurred on Monday. Numerous very large (size 3) avalanches were reported in the Selkirks, including neighbouring Glacier National Park. These layers occurred at all aspects and elevations and involved both storm slab and deep persistent slabs.
The avalanche cycle was less dramatic in the Monashees, where there were primarily size 1 storm slab avalanches. However, there were two notable deep persistent slab avalanches in the Monashees that occurred on open treed slopes at 1750 and 1850 m.
Last week's warm storm produced a similar spike in very large deep persistent slab avalanches. We have ample evidence that this problem remains a very serious concern in the Columbias. Large avalanches will be most likely when this weak layer is stressed by heavy loads or dramatic warming.
20-30 cm of recent snow has likely been redistributed into leeward terrain at upper elevations. 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.
