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 on Saturday
Weather Forecast
Storm systems are expected to impact the south coast all weekend but it looks like the bulk of the snowfall will be confined to the immediate coast. 10-20cm of new snowfall is expected by Saturday morning. Freezing levels are expected to drop to around 1000m and alpine winds are forecast to be strong from south. Another 5-15cm of snowfall is expected on Saturday with freezing levels around 1000m and strong alpine winds from the southwest. Light snowfall is forecast to continue on Saturday overnight and Sunday morning with another 10-20cm of snowfall possible. Periods of clearing are expected between storm pulses over the weekend but there is lots of uncertainty regarding the timing. Unsettled conditions are currently expected for Monday with light snowfall and sunny breaks both possible.
Avalanche Summary
Observations were limited on Thursday due to the stormy conditions but a natural size 2.5 storm slab avalanche was reported from the north of the region. The occurred on southeast through southwest aspects at 2100m and the slab was 70-100cm thick. Some natural activity was reported from the Duffy on northern aspects. Natural activity remains possible on Friday in steep freshly wind-loaded terrain. More widespread storm slabs are expected to remain sensitive to human-triggering, especially on steep unsupported terrain features and wind loaded slopes.
Snowpack Summary
30-60cm 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. Extreme southerly winds have created very 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.