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Avalanche Forecast

Archived

Apr 15th, 2013–Apr 16th, 2013

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

Regions

South Columbia.

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Tuesday: No snow. Moderate E winds. Freezing level near 1300 m. Wednesday: Light snow. Light SW winds. Freezing level near 1500 m. Thursday: Light snow. Light SW winds. Freezing level near 1600 m.

Avalanche Summary

Several size 1 wind slabs were triggered naturally by wind-loading on Monday. Explosives testing in the south of the region produced slabs up to size 2.5 failing on a crust in cliff terrain. A skier triggered a size 2 cornice and loose snow avalanche on a NE aspect at 2400 m on Sunday.Neighbouring regions: In Glacier National Park, skiers triggered a size 3 slab on a buried crust on an east aspect in the alpine on Monday. On Sunday in the North Columbia region, a helicopter remotely triggered a size 3 slab from 50 m away. It failed on a west aspect at 2450 m, on a crust buried down 60 cm. I suspect these were the same interface. This interface also exists in the South Columbia region.

Snowpack Summary

Up to 40 cm recent storm snow has been shifted by variable winds into reactive wind slabs at treeline and above. A weak interface down about 60-120 cm consists of a crust on solar aspects, and surface hoar on high-elevation northerly aspects. Cornices in the region are very large and potentially destructive. Periods of warming or solar radiation may increase the reactivity of cornices and storm slabs.

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.

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.