New storm slabs have developed at higher elevations. Forecast changing wind directions may result in reverse loading.
Confidence
Moderate - Wind speed and direction is uncertain on Friday
Weather Forecast
Overnight: 5-15 cm of new snow with moderate southwest winds and freezing down to 800 metres. Friday: Overcast with another 5-8 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 1500 metres. Sunday: Mostly sunny with light winds and daytime freezing up to 1900 metres.
Avalanche Summary
Thin storm and wind slab avalanches were reported up to size 1.5 early in the storm on Wednesday. One deep persistent slab avalanche size 3.0 was reported on Tuesday from the Selkirks, there was no information regarding aspect or elevation. Natural cornice falls were reported up to size 3.0 on Monday.
Snowpack Summary
The new storm slab is now 20-30 cm deep, and the snow arrived with east or southeast winds. The wind is forecast to change to the west, and this may result in reverse loading. This new now is sitting on the 30-50 cm of recent snow from the past week. The new and recent snow are covering a mix of old surfaces, including several crusts on all aspects at treeline and below, and on solar aspects in the alpine. Cornices continue to be reported to be large and fragile, and the have released naturally 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. Yet another deep release was reported in the region on Saturday. This activity, although growing more sporadic, is keeping these layers an ongoing concern. They 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.