South Columbia

Another wave of new snow is keeping avalanche danger elevated in the South Columbia mountains.

Moderate - Intensity of incoming weather systems is uncertain

Thursday: An incoming storm wave will deliver 15-25cm of new snow. Strong southwest winds. Freezing level rising to 1000 metres with alpine temperatures to -6.Friday: Cloudy with isolated flurries and a trace of new snow. Winds moderate gusting to strong from the northwest. Freezing level dropping to around 700 metres with alpine temperatures to -8.Saturday: Cloudy with isolated flurries and a trace of new snow. Winds light from the southwest. Freezing level dropping to valley bottom with alpine temperatures to -9.

Avalanche observations have begun to emerge from observers getting out into the mountains since the recent storm. Explosives control and slope cutting has yielded numerous size 1-1.5 results in the storm snow, with one explosive result to running size 2 with a 200 metre-wide crown. Crown depths have averaged between 25 and 60cm. Reports of natural avalanches are still limited to a single size 1.5 wind slab avalanche, but strong ridgetop winds on Wednesday along with new snow on Thursday will promote ongoing slab formation. For the short term, I also expect loose dry avalanches to be triggered easily in steep sheltered terrain. Of note, two skier triggered size 2 avalanches were recently reported in the Roger's Pass area. Both are reported to have slid on the mid-December weak layer. Although they took place in an adjacent forecast region and could be considered isolated, a possible pattern of increasing activity on the mid-December layer bears mentioning in the South Columbia region as well.

Between 30 and 75cm of new low density snow has fallen over the region since Monday. The highest accumulations have occurred in the Monashees. Expect new wind slab formation on lee features in higher elevation terrain where the winds were stronger. In areas sheltered from the wind, the new snow is mostly loose and unconsolidated. 50-90 cm below the surface you'll find the mid-December interface which consists of wind affected snow, faceted (sugary) crystals, and/or surface hoar crystals. Recent tests suggest the the new snow is well bonded to the interface in most areas. However, this layer is still reactive in some snowpack tests and should be investigated before pushing into steeper terrain. Limited observations from the North Columbia region suggest this layer may be especially touchy on the eastern side of the Selkirks. The thick mid-November crust layer typically sits 1-2 m down in the snowpack. Recent test results on this layer suggest it is generally well bonded to the adjacent snow with the possible exception of shallow snowpack areas. This layer is considered dormant at this time but remains an isolated concern that we will likely be tracking through much of the season.