Adopt a cautious mindset with terrain today - large avalanches remain possible due to strong south winds, 15-45 cm of new snow & a known weak layer. Reactive wind slabs will likely form in the lee of windy ridge crests and exposed treeline features as winds increase to strong.
A weak layer of surface hoar, now about 40-70 cm deep, may be possible to trigger on sheltered, shaded slopes near treeline (above 1700 m). Recent activity on this layer has been most notable in the southern half of the region. Concern for this problem is increasing in line with loading from new snow and increased avalanche activity in shallower snowpack layers.
A critical load of new snow(15-45 cm) has accumulated above a recently buried surface hoar weak layer in many parts of the region. Avalanche conditions are expected to become increasingly touchy as the new snow settles and forms cohesive slabs over this layer. Areas where wind loading has occurred are especially concerning.
Active weather will bring light to moderate snow, warmer temperatures and increased wind Saturday night into Monday. Heavier snowfall levels and warmer temps are forecast for the south of the region.
Friday night: Mainly cloudy with clear periods and isolated flurries, trace new snow, light southwest treeline wind, alpine low temperatures around -10 C. Freezing level valley bottoms.
Saturday: Cloudy with isolated flurries, trace to 5 cm new snow, light to moderate southwest wind, increasing to strong overnight, alpine high temperatures around -6C. Moderate snow forecast overnight Saturday with up to 15 cm in the southern areas. Freezing level rising to 900 m.
Sunday: Snow, 10-30 cm of new snow, moderate southeast treeline winds, alpine high temperatures around -5C and freezing level 900-1300 m.
Monday: Heavy snow, 10-30 cm of new snow during the day tapering overnight with an additional 2-5 cm forecast. Highly variable moderate to strong westerly wind. Alpine high temperatures around -3C. Freezing level 900-1500 m.
On Friday, less activity was reported by the time of publishing but operators continue to report on the recent natural and skier triggered cycle to size 2.5 in recent storm snow. Ongoing reports of loose dry avalanches (sluffs) in steep terrain continue to be submitted, which is further evidence of how slippery the surface hoar layer is and how reactive it might be once more slab properties exist in the snowpack.
On Thursday, there were reports of touchy conditions and a widespread avalanche cycle including numerous skier triggered small avalanches (size 1-1.5) and a few larger skier triggered and natural avalanches (size 2-2.5). The most activity was reported on northern aspects near treeline (1900-2200 m) where storm slabs failed on surface hoar. Other avalanches were reported in higher wind affected terrain and also where new snow sits on top of a nasty combo of surface hoar or facets over sun crust.
Another persistent slab avalanche (size 1.5) was intentionally triggered by a skier in the Valhallas on Wednesday. This occurred on a steeper north aspect at 2150 metres, where the failure plane was about 30 cm deep. This follows a recent pattern of isolated releases on this layer in this region.
Widespread slab avalanches were reported in areas that had larger total snowfall accumulations, hinting at what will happen everywhere as forecast snowfall amounts increase Saturday night. Significant loose dry avalanches (sluffs) continue to be reported in steep terrain where no slab properties exist. In some areas these loose dry avalanches have triggered larger slab avalanches in step-down events.
Variable storm tracks resulted in 15-45 cm of recent new low density snow that had fallen by Friday from the past few days. The highest levels were reported in more mountainous regions in the central and southern zones of the region. Low density recent snow will be easily transported by moderate winds in exposed treeline and in the alpine building reactive wind slab and wind effect. Recent wind was light to moderate from the southeast, but is forecast to shift to moderate to strong southwest mid-day on Saturday.
Density layers within the recent snow have been reported. The new snow has buried a widespread layer of surface hoar that was reported as up 10 mm in sheltered areas around treeline and below treeline. This surface hoar grew on a variety of surfaces that include wind affected surfaces in exposed terrain, a thin sun crust on steep solar aspects, as well as more variably wind affected and faceted snow in more sheltered terrain. Below 1700-1800 m, 20-50 cm of snow is settling above a decomposing melt freeze crust.
Observers continue to find a preserved layer of surface hoar down 35-70 cm in sheltered, open slopes at and below treeline. Most recent reactivity has been reported in the Selkirks and Valhallas toward the south of the forecast region (see avalanche summary). There is concern for the areas this layer remains preserved now that it is being stressed by a significant load of new snow.
Deeper in the snowpack, a couple of older persistent weak layers may still be identifiable from late and early December, consisting of surface hoar and a crust with faceted snow and buried anywhere from 100-200 cm deep. Prolonged periods of inactivity and unreactive snowpack test results suggest that these layers have trended towards dormancy.
