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Avalanche Forecast

Archived

Nov 26th, 2012–Nov 27th, 2012

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

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

Weather Forecast

Synopsis: A ridge of high pressure over southern BC should maintain dry conditions on Tuesday; however, expect thickening cloud as a frontal system approaches the region from the west. The system should give moderate precipitation on Wednesday and Thursday. Tuesday: Increasing cloud with flurries possible late in the day. Freezing level at around 500 m. Winds light from the southwest. Wednesday: Periods of snow – 10-20 cm. Freezing level steady at around 300 m. Thursday:  Periods of snow or flurries – 5-10 cm. Freezing level at the surface.

Avalanche Summary

A few small natural slab avalanches were reported in the Shames backcountry on Sunday. These were generally 20 cm deep, failing within the recent storm snow. Some larger avalanches (up to size 2.5) were also observed in surrounding areas. Slope testing on several small steep slopes on Sunday afternoon produced no results. Human triggered avalanches remain possible on Tuesday, particularly in exposed wind loaded terrain. The potential for natural avalanches may increase again on Wednesday with more snow and stronger winds forecast.

Snowpack Summary

60-80 cm of storm snow fell in the past few days, accompanied by shifting south to northwest winds. Weaknesses may exist within or under the storm snow. Expect deep wind slabs in exposed lee terrain and in cross-loaded gullies or terrain features. A recent profile at 1200m in the Shames area showed a thin layer of facets sitting on a crust 35cm off the ground. A snowpack test produced easy results on this layer, but the resistant fracture didn't propagate across the entire column. Total snowpack depth are probably around 150 cm 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.