Recent wind loading and reactive wind slabs are the primary concern. However, as the recent storm snow continues to settle, it will still be important to evaluate the bond between the old snow surface and the new snow.
Summary
Confidence
Moderate -
Weather Forecast
One last pulse of snowfall is forecast on Friday before conditions dry out for the weekend. Around 5 cm of snowfall is expected on Friday with another 5 cm Friday overnight. Alpine winds are forecast to be light from the southeast and treeline temperatures are expected to be around -8C. On Saturday, mostly cloudy conditions are expected with the possibility of lingering flurries in the morning and sunny breaks in the afternoon. Alpine winds are forecast to remain light but shift to a northeast direction and treeline temperatures are expected to be around -10C. On Sunday, mostly sunny conditions are forecast with light alpine wind and treeline temperatures around -15C.
Avalanche Summary
On Wednesday, a natural size 2 storm slab avalanche was reported on an east aspect at 2100 m elevation. Ski cutting and explosives triggered a few wind slab avalanches up to size 1.5. These were 20-40 cm thick. On Tuesday, a skier triggered a small wind slab avalanches at 1900 m. There were a few reports of small natural wind slabs above 2000 m on easterly aspects and explosive controlled avalanches were noted in similar terrain up to size 2.5. On Monday, numerous natural slab avalanches were reported up to size 2.5 on a variety of aspects and elevations.On Friday, the biggest concern remains areas where the recent storm snow has been redistributed into wind slabs. There is also still concern regarding the mid-December interface that was buried during the recent storm. It appears that in most places the recent storm snow is relatively low density and has not formed a slab over this interface. The only areas where this layer has been reactive is in wind loaded areas but I would continually watch for signs that a slab is developing in areas that have not been affected by wind.
Snowpack Summary
Up to 60 cm of recent storm snow sits on a plethora of old snow surfaces including stiff wind affected snow, faceted (sugary) crystals and surface hoar crystals that formed in locations sheltered from the wind. Snowpack tests indicate easy, sudden shears on this interface, indicating a poor bond with the underlying snow. However, so far, avalanches associated with this layer have been relatively small (size 1 to 2) and mostly limited to windy areas or unsupported features. This may change as the upper snowpack starts to become stiffer and denser - if it does we may start to see wider propagation resulting in the potential for larger avalanches. Telltale signs of this will be whumpfs or remote-triggering of avalanches from flat terrain. The thick mid-November crust layer typically sits 1-2 m down in the snowpack. Recent test results on this layers have varied from moderate and sudden to hard and resistant, and in many cases no result. This layer is generally considered dormant at this time but remains an isolated concern that we will likely be tracking through much of the season.
rbuhler,
Avalanche Canada
