Avalanche Forecast

Issued: Nov 25th, 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 and Wind Slabs.

Peter, Avalanche Canada

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.

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 2500 m. Winds light from the northwest. Wednesday: Increasing cloud with precipitation developing. Freezing level around 1800-2000 m.

Avalanche Summary

Recent observations are from the Whistler area: Several natural avalanches up to size 2 were observed during the storm on Friday and Saturday morning. Most of these avalanches failed within or below the storm snow. Recent avalanche control 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 main snowpack feature worth noting is a rain crust buried in early November that is now down around 80 cm at treeline and as deep as 150 cm in alpine areas. A weak layer of facets on top of and within this crust is worth remaining suspicious about (sudden collapse fracture character in snowpack tests showing propagation potential). 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

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.

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

Wind slabs below ridgecrests, behind terrain features, and in cross-loaded gullies may remain 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.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

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