Watch for newly formed wind slabs on Friday. These may exist at surprisingly low elevations in areas that saw the most new snow and strongest wind on Thursday. The north of the region is the greatest concern for both of these factors.
Recent moderate to strong winds have created new wind slabs with loose surface snow. This problem is expected to be touchiest in the north of the region where substantial new snow was available for new slab formation.
Two layers that cause concern in the northern part of the region include:
Thursday night: Cloudy with isolated flurries with a trace to 5 cm of new snow. Light to moderate southwest winds.
Friday: Mainly cloudy. Light to moderate southwest winds. Alpine high temperatures around -14.
Saturday: Cloudy with flurries bringing 3-5 cm of new snow, continuing overnight. Light to moderate south winds. Alpine high temperatures around -7, closer to -4 in the south of the region.
Sunday: Cloudy with easing flurries and a trace of new snow. Light to moderate south winds. Alpine high temperatures around -2, closer to 0 in the south of the region.
Reports from the region have been limited during the cold snap, however a MIN from Tuesday describes winds actively forming new slabs in the Duffey area. Similar conditions were observed in the Coquihalla area:
On Monday small wind and storm slabs to size 1.5 were observed in the recent storm snow. Interesting to note that wind slabs were observed in open treeline features which speaks to the widespread nature of Sunday's north wind event.
On Saturday, the snowpack was reactive to explosive triggers. Some avalanches stepped down to a feathery surface hoar layer buried 50-60 cm deep.
Last Thursday, explosive control work produced a size 2 avalanche off the Duffey Lake road that released on the mid November facet/crust layer.
About 20 cm of new snow accumulated in the north of the region during the midweek storm, with only a trace of new snow in the south of the region. Moderate to strong winds redistributed loose surface snow, (new snow in the north, old snow in the south) into new wind slabs on Wednesday night and Thursday.
This new snow and new wind slab is layered above an older layer of wind-affected snow from the recent arctic outflow event.
A deep persistent weak layer remains a serious concern at the bottom of the snowpack in the northern half of the region (e.g., Duffey, Hurley). It's made up of sugary faceted grains and a hard melt-freeze crust. This layer is most likely to be triggered in thin, rocky features where it exists closer to triggering forces on the surface.
There are currently no concerns about deep weaknesses in the snowpack near Coquihalla summit and elsewhere in the south of the region.
