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Avalanche Forecast

Archived

Jan 11th, 2013–Jan 12th, 2013

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

Regions

Kootenay Boundary.

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Saturday: Light winds out of northwest.  Freezing level at valley bottom.  No significant snowfall. 1500m temp: -10Sunday: Light winds out of northwest. Freezing level at valley bottom.  No significant snowfall.  1500m temp: -10Monday: Moderate W winds at ridgetop in the AM, increasing to strong W after lunch.  Freezing level at valley bottom.  Isolated flurries, no significant accumulation.Tuesday:  Freezing level forecast to rise to 2000+m

Avalanche Summary

Widespread avalanche cycle at and below treeline to size 1.5 on Thursday.  Explosive control work (large trigger) initiated avalanches to size 2.5 on SE through E facing slopes around 2000m.

Snowpack Summary

10 cm of light density snow fell Thursday adding to the 60 cm of rapidly settling storm snow that rests on the January 4th interface which consists of small facets, surface hoar (up to 12mm) in sheltered treeline and below treeline areas and sun crust on steep south and west facing slopes. The bonds with the facetted snow are improving while the surface hoar &/or sun crust interface is weak.  Recent tests show Resistant Planar shears on this layer in the alpine, but easy/sudden shears persist at and below treeline.Previous SW winds redistributed the new snow (dramatically in some areas) to create widespread wind slabbing on lee and open features in the alpine and exposed treeline. Where the wind has been strongest, wind slabs are much lower on slopes than normal.The midpack is well bonded and strong. The November 28 surface hoar is still being found in isolated, sheltered below treeline locations buried 120cm. The deep crust/facet combo from early November still exists and concern remains (although unlikely) for triggering this layer from a shallow spot or with a heavy load.

Problems

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.

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.