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Avalanche Forecast

Archived

Nov 26th, 2012–Nov 27th, 2012

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

Regions

Sea To Sky.

This bulletin is based on limited data. Local variations in conditions are likely to exist. Check out the forecaster's blog for further details on interpreting early season bulletins.

Confidence

Fair - Timing of incoming weather is uncertain

Weather Forecast

Synopsis: A ridge of high pressure should maintain sunny skies for Tuesday before giving way to a frontal system on Wednesday. Tuesday: A mix of sun and cloud. Freezing level at around 1400 m (an above freezing layer between 1800-2200 m  is possible). Winds light from the south. Wednesday: Increasing cloud with precipitation developing. Expect 5-15 cm overnight. Freezing level around 1800m, lowering to 1500 m overnight. Thursday: Moderate to heavy precipitation – 25-40 cm. Freezing level around 1500 m. Winds should be moderate to strong from the south-southeast.

Avalanche Summary

Recent observations are from the Whistler area: Avalanche control late last week did produce isolated results up to size 2.5 that failed on the early November crust/facet layer. 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.

Snowpack Summary

The snow surface consists of surface hoar (10mm), a thin sun crust, and dry snow depending on aspect. A storm snow instability has been noted down 30 cm, giving consistent moderate "pops" results in snowpack tests. The early November facet/ crust layer is now down around 120 cm in the Whistler area. Snowpack tests continue to show sudden collapse (or "drops") results on this layer. Widespread whumpfing and cracking on this layer has also been reported from the Whistler area. 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.). The total snowpack depth at treeline is around a 120 cm. Alpine areas are deeper but more variable. Most slopes below treeline are still below threshold depths for avalanches. For more information check out the telemarktips.com forum , the Mountain Conditions Report, and Wayne Flann's Avalanche Blog.

Problems

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.