Avalanche Canada ccampbell, Avalanche Canada

Sea to Sky Avalanche Forecast

Nov 22nd, 2012 8:12AM

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

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 for the entire period

Weather Forecast

Friday: Moderate to heavy snowfall starting Thursday night is expected to bring 25-35cm of new snow, or more for immediate coastal areas, before tapering off by the evening. Freezing levels could spike as high as 1400m or higher, but shouldn't hover that high for very long. Mountaintop winds are expected to be extreme southwesterlies during the height of the storm. Saturday: Cloudy with isolated flurries, freezing levels around 900-1100m and light to moderate southwesterly winds. Sunday: A mix of sun and cloud, Freezing levels dropping as low as 500m and light winds.

Avalanche Summary

Avalanche control on a northeast facing alpine slope with smooth ground cover in the Whistler area yesterday produced size 1 avalanches running within the recent storm snow and size 1.5 avalanches running on the early November facet/crust weakness. These persistent slabs were particularly sensitive to human triggering on slopes that had previously avalanched naturally last weekend and had since been reloaded. Natural avalanche activity followed by human-triggered activity generally occurs with every intense weather period, such as what's forecast for Thursday night and Friday.

Snowpack Summary

The total snowpack depth at treeline is around a metre, The alpine snowpack is generally deeper, but likely variable with fat drifts and boney rocks, while most slopes below treeline are likely still below threshold depths for avalanches. Although weaknesses exist within the recent storm snow, the main snowpack feature is a rain crust buried early November and now down around 80cm at treeline as as deep as 1.5m in alpine areas. A weak layer of facets on top of and within this curst recently gave very easy sudden collapse compression test results as well as moderate extended column test results that propagated across the entire column. 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.). For more information check out the telemarktips.com forum and the Mountain Conditions Report.

Problems

Wind Slabs

An icon showing Wind Slabs

Likelihood

Likely

Expected Size

1 - 3
Fresh wind slabs below ridgecrests, behind terrain features, and in cross-loaded gullies are expected to be sensitive to human triggers. Particularly where they are sitting on a previously exposed or lightly buried crust from early November.
Assess start zones carefully and use safe travel techniques.>Avoid freshly wind loaded features.>

Aspects:

North, North East, East, South East, South.

Elevations:

Alpine, Treeline.

Persistent Slabs

An icon showing Persistent Slabs

Likelihood

Possible

Expected Size

2 - 4
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.
Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>

Aspects:

All aspects.

Elevations:

Alpine, Treeline.

Valid until: Nov 23rd, 2012 2:00PM