Avalanche Forecast

Issued: Nov 25th, 2012 8:48AM

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

Peter, Avalanche Canada

South Coast.

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

Poor - Due to limited field observations

Weather Forecast

Synopsis: A ridge of high pressure over southern BC should give mainly sunny skies for Monday and Tuesday. The ridge should break down on Wednesday allowing a mild frontal system to push in. Monday: A mix of sun and cloud. Freezing level near surface with a potential above freezing layer developing. Winds are light and variable. Tuesday: A mix of sun and cloud. Freezing level at around 2300 m. Winds light from the northwest. Wednesday: Increasing cloud with precipitation developing. Freezing level around 1800 m.

Avalanche Summary

There are no new reports from the region. Natural avalanche activity was likely during the storm on Friday and Saturday morning. Cooler and drier conditions should decrease the likelihood of natural activity, but human triggered avalanche remain possible, particularly on exposed wind loaded slopes and cross-loaded gullies.

Snowpack Summary

Recent storm snow has probably settled and strengthened under cooler temperatures. Dense wind slabs may still be susceptible to triggering in steep lee terrain. 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.). Coquihalla Pass has 100 cm on the ground, and Cayoosh Pass has about 50cm. Treeline areas have around 100-120 cm, and alpine areas likely have more snow, but also highly variable depths depending on wind exposure. For more information check out the telemarktips.com forum, the Mountain Conditions Report, and Wayne Flann's Avalanche Blog.

Problems

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

Unlikely - Possible

Expected Size

2 - 5

Wind Slabs

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.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Valid until: Nov 26th, 2012 2:00PM