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Avalanche Forecast

Archived

Nov 27th, 2012–Nov 28th, 2012

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Northwest Coastal.

Avalanche danger is set to increase with more stormy weather.

Confidence

Poor - Due to limited field observations for the entire period

Weather Forecast

Wednesday: Snow with 15-20cm of accumulation, freezing levels around 300m, and moderate southeasterly winds. Thursday: Another 15-25cm of snow, freezing levels down to sea level, and moderate to strong southeasterly winds. Friday: Continued snowfall with another 5-10cm, freezing levels remaining at sea level and strong southeasterly winds.

Avalanche Summary

A report from the Shames backcountry on Monday includes more evidence of Saturday's natural avalanche cycle with slab avalanches up to size 3.0 running to mid-runouts. One 30-60cm thick Size 1.5 storm slab ran on a south aspect at 1300m, while a Size 3.0 avalanche was observed on a north-northeast aspect at 1500m, which may have been a thick wind slab or possibly released on a facets near the ground. Human triggered avalanches remain possible, particularly in exposed wind loaded terrain, and natural avalanche activity will likely pickup again with more snow and wind in the forecast.

Snowpack Summary

Recent reports include weaknesses within the 60-80cm of storm snow from late last week; however, the recent cooling trend has likely helped stabilize these storm snow weaknesses A profile at 1200m in the Shames area showed a thin layer of facets sitting on a crust 35cm off the ground. An Extended Column Test produced easy results on this layer, but the resistant fracture didn't propagate across the entire column. Total snowpack depth is probably around 150cm in most treeline areas and deeper but more variable in the alpine. The snowpack below treeline may still be below threshold depth for avalanches in some areas. Check out the Skeena/ Babine discussion forum for more information from the area.

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.