Buried weak layers may be more reactive as temperatures rise over Thursday night and Friday.
Continue to be conservative with terrain choices, stick to simple slopes watch for signs of instability.
Northerly winds are expected to have developed fresh, reactive wind slabs in the alpine and treeline. These slabs are expected to form on southerly aspects and may bond poorly to the underlying crust.
Wind slabs have the potential to step down to the mid-November weakness in the middle of the snowpack, resulting in large avalanches.
Last week's storm buried a weak layer of surface hoar, which has been the culprit for several skier-triggered avalanches in the past week. This layer is now buried 40-70 cm down and is most likely to exist in sheltered and shaded locations.
Weak facets above a crust buried deep in the snowpack may become more sensitive to triggering with the additional load from last week's storm and rising temperatures throughout this week. Small avalanches or large cornice falls could step down to this layer resulting in large, consequential avalanches.
On Wednesday, a natural size 2 wind slab avalanche was reported. As northerly winds are expected to continue, natural and rider triggered wind slabs remain possible.
During the storm last Friday, natural and skier triggered avalanches were reported to size 2. Explosive control produced persistent slab avalanches that failed on the mid-Nov crust down about 50cm.
Over the weekend, many riders in the Squamish and Whistler area were surprised by size 1-2 slab avalanches. These slabs mainly occurred on wind-loaded slopes on north and west aspects in the alpine and treeline.
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Pockets of wind slabs have developed from northerly winds at higher elevations. Expect rising temperatures will break down the surface snow on all aspects, creating a widespread crust below 2500 m once the cooling trend begins on Friday evening.
A layer of surface hoar from early December is buried 30-50 cm deep below more wind affected snow. This surface hoar remains a concern, preserved in shaded and sheltered terrain features.
The primary concern within the snowpack is a crust buried in late November, with weak facets sitting above. Professionals are concerned about the possibility of avalanches releasing at this deeper interface with the new snow load and warm temperatures.
Total snow depths remain low for December with 90 to 140 cm at treeline and up to 200 cm in the alpine. Much of the below treeline elevation band is below the threshold for avalanches.
Thursday Night
Clear skies. Moderate northerly winds. An above freezing layer of air sits around 1500-2000 m,
Friday
Clear skies. Alpine temperatures reach a high of 3 °C. Moderate northwest winds. An above freezing layer of air sits around 1500-2500 m.
Saturday
Mainly cloudy with isolated flurries. Alpine temperatures reach a high of -5 °C. Freezing level at valley bottom. Moderate to strong northwest winds at ridgeline.
Sunday
3 cm possible overnight.
Partly cloudy with moderate westerly winds at ridgeline. Freezing level below valley bottom, alpine high of -15°C. Another 3 cm of snow possible over the day.
More details can be found in the Mountain Weather Forecast.
