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Avalanche Forecast

Archived

Dec 23rd, 2011–Dec 24th, 2011

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 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.

Regions

South Coast.

Confidence

Fair - Intensity of incoming weather is uncertainfor the entire period

Weather Forecast

Saturday: 3-5cm of snow - moderate to strong southwest winds - Freezing level at 1200mSunday: 8-12cm of snow arriving late in the day - moderate southwest winds - freezing level at 800mMonday: 8-12cm of snow - light to moderate southwest winds - freezing level at surface

Avalanche Summary

Fresh wind slabs and cornices are sensitive to human-triggers A size 2 windslab was ski cut yesterday on Vantage Peak on the Duffey Lake area (alpine elevation band-northeast aspect)

Snowpack Summary

Dribs and drabs of new snow, in the Coquihalla area, with associated winds are keeping wind slabs fresh and poorly bonded, but also keeping recent surface hoar development and distribution to a minimum. While in the Duffey Lake area, wind-exposed slopes are predominately scoured and pressed, with pockets of hard wind slab. Buried surface hoar and/or facets persists 10 or so centimetres below a weak rain crust on sheltered treeline slopes and below, where recent compression tests on a northerly aspect at 1750m produced easy sudden results down 20cm on surface hoar as large as 15mm. The mid and lower snowpack are generally well-settled and strong, but recent reports suggest basal facets create a deep persistent slab problem that deserves caution in shallow snowpack areas on planar rocky slopes.

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.