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Avalanche Forecast

Dec 7th, 2011–Dec 8th, 2011
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low

Regions: Sea To Sky.

Confidence

Fair - Due to limited field observationsfor the entire period

Weather Forecast

The current weather pattern is expected to hold Thursday and Friday with a temperature inversion bringing above freezing temperatures to alpine elevations. The associated valley cloud is expected to blow out Wednesday afternoon with moderate northerly outflow winds, resulting in sunny skies at all elevations. A week frontal system is expected for Saturday with increasing cloud and a chance of light precipitation and moderate westerly winds.

Avalanche Summary

Avalanche activity has tapered off throughout the week. Although the likelihood of triggering deep persistent slab avalanches is low, the potential consequences are still very high.

Snowpack Summary

Surface hoar is growing, surface snow is faceting, and pockets of weak wind slab may still be lingering on various aspects in the alpine.Warm temperatures and sun-exposure likely resulted in a surface crust on steep south aspects. Last weekends rain crust is down 20-40cm and extends up to treeline elevations. Basal depth hoar with an associated crust is prevalent in thin snowpack areas, and especially problematic where it is overlying summer firn. Above that, and down 1-2m, are two more crusts mixed with facets, depth hoar, and surface hoar. Recent compression tests in a shallow snowpack area produced moderate sudden collapse results on this deep persistent weakness. Time has allowed the overlying snow to gain strength making it less likely to trigger the deeper weaknesses, but if you do hit the sweet spot, such as a shallow area, the resulting avalanche could have very serious consequences.

Avalanche Problems

Wind Slabs

Weak wind slabs may still be lurking below ridge crests, behind terrain features, and in cross-loaded gullies.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 3

Deep Persistent Slabs

The right trigger (big air onto steep unsupported slope, sled track trenching deep in a thin area) could have disastrous consequences. The greatest concern is in the Whistler area on slopes with variable snowpack depths above 1900m.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 2 - 7