Hazard will build to Considerable throughout the day with forecast 10-25 cm forecast snow and moderate to strong south wind. Watch for signs of instability like shooting cracks, natural avalanches or settlements (whumps) and make cautious terrain choices.
A weak layer of surface hoar, now about 45-80 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.
25-60 cm of snow by Sunday afternoon will sit on top of a known weak layer of surface hoar, facets and crusts. Within this new snow lies a second smaller surface hoar in addition to temperature and density changes that all may serve as failure planes. Avalanche conditions are expected to become increasingly touchy anywhere recent snow forms cohesive slabs due to wind loading or warming temperatures below treeline.
An offshore low will push bands of warm air and precipitation in upcoming days that are challenging to forecast the precise timing, temperatures and total snowfall amounts.
Saturday night: Snow, 5-15 cm, light treeline south wind gusting strong, with strong south to extreme south wind in the alpine, alpine low temperatures around -6 C. Freezing level 600 - 1200 m.
Sunday: Snow flurries, 5-10cm, light to moderate southwest switching to southeast wind, with strong to extreme south wind in the alpine, alpine high temperatures around -4C. Freezing level 1000 - 1500 m.
Monday: Heavy snow, 10-30 cm, variable light southwest wind gusting strong, alpine high temperatures around -3C. Freezing level 900-1500 m.
Tuesday: Snow flurries, 5 - 10 cm, moderate to strong southwest wind, alpine high temperatures around -4C. Freezing level 900-1200 m.
Avalanche activity has tapered on Friday and Saturday with a cessation of new snow inputs, light wind and cool overnight temperatures. Small soft slab avalanches continue to be triggered in isolated locations around treeline where recent snow laid on top of a weak surface hoar or crust. 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 or on souterhly aspects were recent snow sits over a sun crust. Other avalanches were reported in higher wind affected terrain.
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.
Forecast 10-25 cm of new snow Saturday night into Sunday will fall on a small layer of Surface Hoar (3-6 mm) that formed overnight on Friday. This brings a total of 25-55 cm snow that overlies another known weak layer of large surface hoar (up to 10 mm) and crust, which is showing signs of instability in easy sudden results in test pits, whumphing and isolated avalanche activity. This surface hoar was most intact at and below treeline and sits 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 in the southern Selkirks and Valhallas continue to find a preserved layer of surface hoar down 35-70 cm in sheltered, open slopes at and below treeline, and continued isolated avalanches (see avalanche summary). Deeper in the snowpack, a couple of older persistent weak layers may still be identifiable. The first is from December consisting of decomposing surface hoar and a crust (buried 100-15cm) and the second from early November consisting of a series of crusts with faceted snow (closer to the ground). Prolonged periods of inactivity and unreactive snowpack test results suggest that these layers have trended towards dormancy, but they remain on the radar with forecast signifiant precipitation.
