Storm slabs continue to be a concern. Wide fracture propagations are possible where the storm snow is sitting on a weak buried layer of surface hoar.
Confidence
Moderate - Freezing levels are uncertain
Weather Forecast
A clearing and cooling trend should bring freezing levels down to valley bottoms overnight. A mix of sun and cloud on Monday with periods of light precipitation and moderate westerly winds. A mix of sun and cloud on Tuesday with light winds. A diurnal freeze/thaw cycle setting up with freezing down to valley bottoms overnight and then rising up to 1500 metres during the day. No change for Wednesday, but a new system moving into the region on Wednesday night.
Avalanche Summary
Natural avalanches continued to release down 40-60 cm on Friday up to size 2.5, and on Saturday up to size 3.0. Reports from Thursday that several natural size 2.0 slab avalanches and one size 3.0 storm slab were suspected to have released on the late February surface hoar layer. There was also a report of a size 3.0 avalanche remotely triggered by a skier that was 20 metres away.
Snowpack Summary
New snow continues to develop the storm slab that is 40-60cm thick and bonding poorly to a crust on previously sun-exposed slopes and surface hoar (February 27th or late February) on shady and sheltered slopes. Thicker and touchier wind slabs are lurking throughout exposed terrain at and above treeline. A couple of sun crusts might exist in the upper 50-70cm on southerly aspects. The surface hoar and/or crust layer which was buried February 10 is now down around a metre and is still producing isolated hard sudden results in snowpack tests. Large cornices will be getting weak with warmer temperatures.
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
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.