Snowfall amounts overnight are uncertain and may be higher in western upslope areas. We are also unsure of when and where the sun will shine. Solar radiation on dry storm snow is a concern for increased avalanche activity.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
Light winds and 10-15 cm of new snow overnight. Winds becoming moderate from the northwest during the day on Saturday as a weak ridge of high pressure builds after the storm. There may be some sunny breaks Saturday afternoon, but more likely to clear overnight. Freezing levels bouncing between valley bottoms and 1400 metres. Mostly sunny on Sunday with light winds and freezing levels up to 1200 metres. Cloudy with increasing southwest winds on Monday.
Avalanche Summary
On Thursday there were reports of natural and skier accidental storm slab avalanches up to size 2.0. On Wednesday a ski cut resulted in a size 3.0 avalanche with wide propagation on buried surface hoar above the February 10th crust. Several small skier accidental avalanches and skier controlled avalanches in the storm snow were also reported. On Tuesday there were several skier accidental avalanches up to size 2.0 that released on the storm slab/crust interface. Skier controlled storm slab avalanches up to size 1.5 were mostly on east aspects at treeline. On Monday we had reports of natural wind slab and storm slab avalanches up to size 3.0 and accidentally triggered slab avalanches up to size 1.5.
Snowpack Summary
Up to 35 cm of new snow was reported from the west slope of the Monashees on Friday morning. Recent new snow and wind have developed storm slabs that are 60-90 cm deep. These storm slabs are sitting on a buried melt-freeze crust on east thru west aspects in the alpine, and on all aspects at treeline. In some areas there is a weak layer of surface hoar at the interface between the storm snow and the crust. Moderate winds have created areas of wind slab in the lee of west or southwest winds that may be close to a metre deep. Wind slabs in motion may trigger the storm slab on the crust and result in wide propagations and very large avalanches. The bond between the recent storm snow and the crust is variable across the region, east thru southeast aspects have been the most reactive over the past few days. Surface hoar buried in early January now lies up to 200cm below the surface and has become less of a concern. Possible triggers for this deep and destructive layer include a large cornice fall or significant warming.
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.