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Avalanche Forecast

Archived

Nov 22nd, 2012–Nov 23rd, 2012

Alpine
Below Threshold.
Treeline
Below Threshold.
Below Treeline
Below Threshold.
Alpine
Below Threshold.
Treeline
Below Threshold.
Below Treeline
Below Threshold.
Alpine
Below Threshold.
Treeline
Below Threshold.
Below Treeline
Below Threshold.

Regions

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.

Confidence

Poor - Due to limited field observations for the entire period

Weather Forecast

Friday: Moderate snowfall starting Thursday night is expected to bring 20-30cm of new snow before tapering off by the evening. Freezing levels could spike as high as 1400m, or higher in the Coquihalla, 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 800-1000m and light to moderate southwesterly winds. Sunday: A mix of sun and cloud, Freezing levels dropping to 500m and light winds.

Avalanche Summary

No recent avalanches have been reported, although observations are extremely limited. 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

Coquihalla and Cayoosh Passes have about 50cm of snow on the ground, while treeline areas have around a metre. Alpine areas likely have much more that that but also highly variable depths. The main snowpack feature in the Whistler area is a rain crust buried early November and now down around 80cm at treeline. A weak layer of facets sitting on top of 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. This weakness was  found in the Duffey Lake area as well; however, at least at 1700m it was only 10cm off the ground and still moist. At upper treeline and alpine elevations it may be frozen and faceted and high enough off the ground to reduce the affects of ground cover at least 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

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.