Ongoing snowfall and strong southerly winds will add more load to already thick storm slabs and large cornices. Conservative terrain selection is critical this weekend.
Confidence
Moderate - Intensity of incoming weather systems is uncertain
Weather Forecast
Another 5-10cm of snowfall is expected Saturday overnight with freezing levels around 1000m and moderate alpine winds from the south. A bit of a break is expected in the morning with another 5cm of snowfall is expected on Sunday afternoon. Afternoon freezing levels are expected to be around 1300m and alpine winds are forecast to be moderate from the south. Light snowfall is forecast to continue Sunday overnight. Mostly dry and cloudy conditions are expected for Monday with snow flurries and sunny breaks both possible. Freezing levels are expected to be around 1300m in the afternoon and alpine winds are forecast to be light from the southwest. A mix of sun and cloud is forecast for Tuesday with freezing levels around 1400m and light alpine winds.
Avalanche Summary
On Friday, two natural cornice triggered storm slabs were reported in the north of the region. One was a size 3 storm slab on a northeast aspect at 2000m and was 100cm thick. It was reported to have run full path to the end of the runout. The other was a size 2 on a northeast aspect at 2200m that was 30-60cm thick. On Thursday, a natural avalanche cycle occurred in the north of the region with storm slabs up to size 2.5 reported. Storm slabs are expected to remain touchy to human-triggering on Saturday and natural activity is possible in freshly wind loaded terrain.
Snowpack Summary
40-70cm of new snowfall has accumulated in sheltered areas with greatest amounts to the north of the region. Weaknesses within or at the base of the new storm snow may need a couple days to settle and strengthen. Strong southerly winds have created deep and dense slabs in lee terrain, probably well below ridge crests, while scouring windward slopes. This intense loading may have overloaded a weak layer of surface hoar buried at the beginning of February. This layer was primarily a concern in the South Chilcotin Mountains. Where it has not been flushed out or squashed, it would be 100-150 cm deep now. Ongoing stormy weather has also encouraged extensive cornice growth.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.