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Avalanche Forecast

Archived

Nov 27th, 2012–Nov 28th, 2012

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

Regions

Sea To Sky.

Avalanche danger is set to rise with stormy weather.

Confidence

Poor - Due to limited field observations for the entire period

Weather Forecast

Wednesday: Snow with 15-20cm of accumulation, freezing levels around 1500m, and moderate to strong southerly winds. Thursday: Snow with 20-40cm of accumulation concentrated in immediate coastal areas, freezing levels around 1400m, and strong southerly winds. Friday: Continued snowfall with another 20-30cm again concentrated to immediate coastal areas, freezing levels remaining at 1400m, and strong southerly winds.

Avalanche Summary

Reports from the Whistler area yesterday include a Size 2.5 deep slab avalanche running on the early November facet/crust combo triggered with small explosives low on the slope. Check out Wayne Flann's Avalanche Blog for more information, including photos. Also of note, there was a report of a size 2.5 skier triggered avalanche on Saturday. This avalanche occurred on a northeast aspect in the alpine. It was triggered from the bottom of the slope, and likely released on the early November layer. Fresh wind slabs have been touchy and wet loose natural point-release sluffs have been observed on sun-exposed slopes.

Snowpack Summary

The snow surface consists of large surface hoar, a thin sun crust, surface facets, moist snow, or preserved storm snow depending on elevation, sun and wind exposure, slope angle, time of day, and aspect; all of which could become weak layers once buried by a sufficiently cohesive slab. A storm snow instability has been noted down 30 cm, giving consistent moderate "pops" results in snowpack tests. Snowpack tests continue to show sudden collapse (or "drops") results on the early November facet/crust deep persistent weakness, but because this weakness is so close to the ground in most areas, associated avalanche activity will likely be limited to slopes with smooth ground cover (e.g. scree slopes, rock slabs, summer firn, glaciers, etc.). For more information check out the telemarktips.com forum , the Mountain Conditions Report, and Wayne Flann's Avalanche Blog.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.