New storm slabs have developed at higher elevations. Changing winds may result in reverse loading.
Confidence
Moderate - Wind speed and direction is uncertain on Friday
Weather Forecast
Overnight: 5-8 cm of new snow with moderate west winds and freezing down to 800 metres. Friday: Overcast with another 3-5 cm of snow combined with moderate west winds and daytime freezing up to 1600 metres. Saturday: Overcast with flurries and moderate west winds and daytime freezing up to 1300 metres. Sunday: Mostly sunny with light winds and daytime freezing up to 1800 metres.
Avalanche Summary
Two deep persistent natural avalanches size 3.5 were reported on Wednesday with fractures that were about 4 metres deep. The december surface hoar weak layer is expected to be the sliding layer. Natural avalanches up to size 3.0 were reported on Tuesday on south thru west aspects in the alpine, it was not mentioned if they were cornice triggered.
Snowpack Summary
The new storm slab is 20-30 cm deep and arrived with east or southeast winds in most areas. The winds are forecast to change to the west, and this may result in some reverse loading and new wind slabs on several aspects. This new snow is sitting on another 30-60 cm of recent snow from the past week. The recent snow buried a mix of old surfaces that include melt-freeze crusts on all aspects at treeline and below, and on solar aspects in the alpine. Cornices are reported to be large and fragile, and reports of natural cornice falls continue on a regular basis. The February weak layers are now down about 170-220 cm and the deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack. These deep weak layers produced large avalanches with cornice falls and other heavy triggers in late March and early April. They remain an ongoing concern and may be more likely to fail on southerly aspects during periods of strong solar radiation.
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.
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.