Avalanche Forecast

Issued: Nov 26th, 2012 8:46AM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is low. Known problems include Persistent Slabs.

Avalanche Canada Peter, Avalanche Canada

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.

Summary

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

An icon showing Persistent Slabs
Large avalanches running on a crust near the base of the snowpack are possible, particularly on slopes with smooth ground cover. Remote triggering and step-down avalanches might be a concern with this weakness.
Whumpfing is direct evidence of a buried instability.>Carefully evaluate and use caution around thin snowpack areas.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 5

Valid until: Nov 27th, 2012 2:00PM