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Avalanche Forecast

Archived

Jan 13th, 2012–Jan 14th, 2012

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

Regions

Purcells.

Confidence

Fair - -1

Weather Forecast

SATURDAY: Light amounts of snow with temperatures cooling to -15. Winds moderate to strong from the west.SUNDAY: Light amounts of snow leading to clearer and colder conditions in the afternoon. Winds light from the north.MONDAY: Cold and clear as arctic air descends from the north. Light northerly winds

Avalanche Summary

Last few days reports include numerous fresh natural wind slab avalanches up to Size 2.5 on southeast through northeast facing alpine slopes suspected to have occurred during a wind-loading event on Tuesday. Cornices have also been failing and could be a heavy trigger for wind and persistent slabs on the slope below. Bugaboos. Xh dropping cornices and mushrooms triggering deep instabilities to grnd in isolated features to sz 2.5

Snowpack Summary

Recent light amounts dry snow has maintained the snow supply for fresh wind slab development and cornice growth.Surface condition in wind-exposed areas is highly variable with scoured areas, sastrugi, and pockets of fresh hard and soft wind slabs. Cold temperatures are promoting surface faceting, and a new batch of surface hoar is probably growing in sheltered areas.The mid-December surface hoar/facet persistent weakness, down 40cm on the eastern side of the range and as deep as 150cm on the western side, is generally producing anywhere from easy results where it's shallow to hard results where it's deeper. But all tests consistently show a high propensity to propagate fractures.Check out this YouTube video posted by the Panorama ski patrol of an ECTP2 down around 40cm on surface hoar: https://www.youtube.com/watch?v=1_NQns2Nuh0. Basal facets remain a concern for human triggering in shallow snowpack alpine areas. When these persistent weaknesses are combined with weak wind slabs, thin trigger points, and other weaknesses within and under the recent storm snow, the result is a highly variable snowpack with the potential for deep slab avalanches, especially from heavy, thin spot, and/or step-down triggers.

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.

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.