Avalanche Forecast

Issued: Nov 24th, 2012 8:35AM

The alpine rating is below threshold, the treeline rating is below threshold, and the below treeline rating is below threshold. Known problems include Persistent Slabs and Wind 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 - Due to limited field observations

Weather Forecast

Synopsis: The weather pattern is changing as a ridge of high pressure builds in from the southwest resulting in drier conditions and slightly cooler temperatures for the next few days. Sunday: A mix of sun and cloud. The freezing level is around 800-1000m. Winds are generally light. Monday: A mix of sun and cloud. The freezing level is around 1000m. Tuesday: Should be another dry day, but the next system is forecast to affect the region beginning on Tuesday night or Wednesday morning.

Avalanche Summary

There are no new reports from the region. There was likely enough snow, when combined with strong winds, that natural avalanches released (wind slabs behind ridges?) in some areas. My suspicion is that natural storm snow avalanches have now ended, but the possibility of triggering a lingering pocket remains this weekend.

Snowpack Summary

There are no recent field observations from the region, however weather stations show enough new snow (25-30 cm in the Coquihalla) which came with enough wind (Moderate to strong from the South) that wind slabs should be expected behind ridges and in cross-loaded terrain. Coquihalla and Cayoosh Passes have about 50cm of snow on the ground, while treeline areas have around a metre. Alpine areas likely have more snow, but also highly variable depths depending on wind exposure. The main snowpack feature is a rain crust buried early November and now down around 80cm at treeline. A weak layer of facets sitting on top of this crust shows "collapse" fracture character and the ability to propagate. Widespread whumpfing and cracking on this layer has also been reported. It's mostly a concern at upper treeline and alpine elevations on slopes with smooth ground cover (e.g. scree slopes, rock slabs, summer firn, grass, etc.). 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 are a concern with this weakness.
Be aware of the potential for full depth avalanches due to deeply buried weak layers.>Whumpfing is direct evidence of a buried instability.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 5

Wind Slabs

An icon showing Wind Slabs
Fresh wind slabs below ridge crests, behind terrain features, and in cross-loaded gullies may be sensitive to human triggers. Particularly where they are sitting on a previously exposed or lightly buried crust from early November.
Use ridges or ribs to avoid pockets of wind loaded snow.>Be cautious as you transition into wind affected terrain.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Valid until: Nov 25th, 2012 2:00PM

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