Avalanche Forecast

Issued: Nov 27th, 2012 3:00PM

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

ccampbell, Avalanche Canada

Northwest Coastal.

Avalanche danger is set to increase with more stormy weather.

Summary

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

Expect to find weak wind slabs below ridgecrests, behind terrain features, and in cross-loaded gullies. Natural avalanche activity is possible with heavy loading from snow and wind and human triggering is likely, especially on steep convex slopes.

Assess start zones carefully and use safe travel techniques.>Avoid freshly wind loaded features.>

Aspects: North, North East, East, South East, South, South West.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 4

Persistent Slabs

Basal facet/crust weaknesses are often prone to remote triggering and step down avalanches, and typical trigger points include thin rocky areas. They may be difficult to trigger, but deep persistent slab avalanches are often very large.

Be aware of thin areas that may propagate to deeper instabilites.>Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.>If your sled is bogging down, don’t spin the track and trigger the weak layer below.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Valid until: Nov 28th, 2012 2:00PM