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Avalanche Forecast

Archived

Mar 10th, 2012–Mar 11th, 2012

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

Regions

Northwest Coastal.

Confidence

Fair - Intensity of incoming weather is uncertain on Sunday

Weather Forecast

Sunday: light snowfall - light southerly winds - freezing level at 400m Monday: trace amounts of snow with some clearing- light southeast winds - freezing level at 400m Tuesday: very light snowfall - light southwest winds - freezing level at 200m

Avalanche Summary

A size 1.5 natural wind slab avalanche was reported on Friday on a cross-loaded slope at treeline. Storm snow avalanches up to size 3.5 were reported from the big terrain around Bear Pass. A few natural size 2 slab releases on the early February persistent weak layer interface were reported on Thursday. They occurred below treeline on steep, unsupported terrain.

Snowpack Summary

Continued strong westerly winds have created widespread reactive wind slabs on lee aspects. A persistent weak layer of surface hoar buried at the beginning of March is as much as 70cm deep and has started to become reactive in some areas. The early February persistent weak layers (surface hoar, facets, crusts) are buried as much as 110cm down and also remain a concern in some parts of the region. Although not widespread throughout the region, persistent slabs would be destructive in nature and may be reactive to human triggers, particularly below treeline on isolated and sheltered steep terrain where buried surface hoar may be preserved. Cornices in the region are reported to be large and unstable.

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.