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Avalanche Forecast

Archived

Apr 4th, 2017–Apr 5th, 2017

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Cariboos.

Cornice falls have been responsible for most of the avalanches reported in the past few days. Wind slabs or cornices may trigger persistent weak layers resulting in large avalanches.

Confidence

High -

Weather Forecast

Overnight: Cloud developing with moderate-strong southwest winds and freezing down to 1000 metres. Wednesday: Strong southwest winds combined with 3-5 cm of new snow and daytime freezing up to 1700 metres. Thursday: Overcast with moderate south winds and a couple of cm of new snow. Daytime freezing level to 1800 metres. Friday: Another 3-5 cm of new snow with sunny breaks in the afternoon and freezing levels around 2000 metres.

Avalanche Summary

Several natural cornice falls were reported on Monday up to size 3.0.

Snowpack Summary

Last week's stormy weather brought up to 40 cm of snow to upper elevations. This storm snow overlies a rain crust below about 2000 metres and a sun crust on solar aspects at higher elevations. Several other temperature and or solar crusts are likely to exist within the storm snow, mainly at lower elevations and on solar aspects. Moderate to strong southwest winds during and since the snowfall formed wind slabs on leeward slopes and promoted the growth of large, fragile cornices along ridgelines. At higher elevations, the February weak layers are down about 120-150 cm and the deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack. These layers were active during a storm in mid-March and produced some very large avalanches. Occasional deep releases were also reported in late March and these deeply buried weaknesses remain a serious concern as solar radiation and warming temperatures begin to penetrate the snowpack at increasingly higher elevations. Cornices and wind slabs are also weakened by these warming effects and have the potential to trigger deeply buried weak layers if they release.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.