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Avalanche Forecast

Archived

Dec 30th, 2011–Dec 31st, 2011

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Northwest Coastal.

Confidence

Fair - Timing or intensity of solar radiation is uncertain on Saturday

Weather Forecast

Saturday: A much drier day, with some light flurries possible. Snow beginning overnight with 5cm possible. Sunshine in some areas. Freezing level 500m. Moderate south-west winds.Sunday: 20cm snow during the day, with another 20cm overnight. Freezing level climbing to 1000m overnight. Moderate to strong southerlies.Monday: 5cm snow. Freezing level 1000m, lowering late on Monday to 500m.

Avalanche Summary

Wind slabs and cornice releases dominated recent avalanche observations. Highways avalanche control produced numerous Size 2-3.5 slab avalanches. The largest of these failed at ground, up to 4m deep.

Snowpack Summary

A relentless pummelling by snow, strong to extreme winds, and fluctuating freezing levels has added around 2m of new snow near Terrace and around 120cm near Stewart. Strong south to southwest winds have created hard and soft wind slabs on lee slopes. Large sensitive cornices also exist.Deeper in the snowpack, buried surface hoar and a crust-facet combo (which extends up to alpine elevations in the south and to 1000m in the north) remain a cause for concern, with the potential for deep, destructive avalanches. Recent observations suggest these layers may be gaining strength, however I wouldn't write them off just yet.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

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.