The recent storm snow remains reactive in wind exposed terrain at higher elevations.
In the Selkirks around Revelstoke, a more widespread storm slab problem may still exist, especially where the recent storm snow overlies a weak layer of surface hoar.
The recent storm snow remains reactive in wind exposed terrain at higher elevations. In the Selkirks around Revelstoke, a more widespread storm slab problem may still exist, especially where the storm snow overlies a weak layer of surface hoar.
The early December crust can be found down 80 to 200 cm below the surface, with a weak layer of facets on top of it. The likelihood of triggering an avalanche on this layer is decreasing but still remains a concern for avalanches stepping down. We are now in a low probability/high consequence scenario with this layer.
A ridge of high pressure brings some clearing before the next system arrives on Sunday afternoon bringing active weather for Monday.
Saturday night: Partly cloudy, light variable wind, freezing levels dropping to valley bottom.
Sunday: A mix of sun and cloud in the morning, cloudy with flurries in the afternoon, winds becoming moderate SW, freezing levels reaching around 800 m.
Sunday night: Snowfall 5-10 cm, moderate SW wind, freezing levels around 600 m.
Monday: Snowfall 5-10 cm, moderate SW wind, freezing levels reaching around 1000 m.
Tuesday: A mix of sun and cloud, light variable wind, freezing levels near valley bottom.
On Friday, explosives triggered a size 2 cornice and several small storm slab avalanches. With better visibility, many operations were continuing to report evidence from the natural cycle on Wednesday/Thursday with numerous very large avalanches occurring in the storm snow. There were also more avalanches reported in the Selkirks which had stepped down to the early-December layer during the storm.
On Thursday, a variety of natural and human triggered storm slab avalanches up to size 3.5 were observed throughout the region on all aspects at higher elevations. These were typically 30-50 cm thick but up to 100 cm in wind loaded areas. At lower elevations, natural loose wet activity was being reported.
On Wednesday, a natural storm slab avalanche cycle occurred at higher elevations. In addition to these storm slab avalanches, a size 3 cornice-triggered persistent slab avalanche was also reported on a NE-E aspect at 2300 m in the Monashees failing on the early December crust/facet layer down 70-100 cm. Just north of the region, an additional three persistent slab avalanches up to size 3.5 were observed during the storm on the same interface down 110-150 cm.
One or two thin new crusts may be found in the upper snowpack which are now buried by 5-10 cm of new snow. The crust appears to be most prominent in the Monashees where it extends well into alpine elevations and possibly all the way to the mountain tops. In the Selkirks, the crust seems less developed and only extends to around 1700-1800 m. In addition to the new crust, a new layer of surface hoar has been reported and is now likely buried under the most recent snowfall. Below the crust and at higher elevations, 25-50 cm of storm snow from the past week is settling rapidly with the mild temperatures. This recent storm snow overlies the January 10 interface which may include weak facets and/or surface hoar. Another layer of facets from early January can be found down 60-90 cm.
The early December crust/facet interface is now typically down 80-150 cm, but as deep as 200 cm in wind loaded terrain. It consists of faceted grains above a bulletproof crust formed by the Atmospheric River rain event at the end of November. There has been avalanche activity on this layer as recently as recently as Thursday, primarily in the north of the region. Heavy triggers like natural cornice falls and storm slab avalanches may still have potential to step down to this layer resulting in very large avalanches.
This video from our field team provides some additional insight into the snowpack in the south of the region.
