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Archived

Avalanche Forecast

Jan 13th, 2012–Jan 14th, 2012
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

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.

Avalanche Problems

Wind Slabs

Weak wind slabs are lurking below ridgecrests, behind terrain features and in cross-loaded gullies.

Aspects: North, North East, East, South East, South, South West.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 3

Persistent Slabs

Most concerning on steep, unsupported slopes, in open glades glades.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 3 - 5

Deep Persistent Slabs

Susceptible to human triggers particularly from heavy impacts or in areas with thin snowpack. If triggered, slabs are likely to release across very wide areas producing highly destructive avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 3 - 6