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 - Timing or intensity of solar radiation is 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 light 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 up to size 2.5 were reported on Saturday. Skier accidental, skier remote triggered, and natural avalanches up to size 2.5 continued to be reported on Friday. Most of these avalanches were releasing in the storm snow, or at the storm snow/surface hoar interface. On Thursday, natural avalanches up to size 2.0 were reported as well as several remotely triggered slab avalanches up to size 2.0. These slides occurred on all aspects, at all elevations, and were generally 40-60 cm deep.
Snowpack Summary
Some reports from the Monashees of a thin melt-freeze crust that has developed within the storm snow that has been reactive up to size 2.0 on Sunday. Variable amounts of new snow and wind have continued to develop storm slabs 40-60 cm thick that are bonding poorly to a crust on previously sun-exposed slopes and surface hoar (February 27th) on shady and sheltered slopes. Thicker and touchier wind slabs are lurking throughout exposed terrain at and above treeline. A weak layer of surface hoar and/or a sun crust buried February 21 is now close to a metre below the surface. Where it exists, this layer may become reactive to human triggers as the overlying slab develops. The surface hoar and/or crust layer buried February 10 is likely down over a metre. This layer was less reactive over the past week with cooler temperatures, but remains a concern for large triggers like cornice falls or a smaller avalanches stepping down. Cornices are large and potentially weak and should be avoided where possible.
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.