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Avalanche Forecast

Archived

Jan 3rd, 2012–Jan 4th, 2012

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 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

South Coast.

Confidence

Good - -1

Weather Forecast

Wednesday: 10-30cm of new snow with freezing levels around 1500m and strong southwesterly winds. Thursday: 5-10cm of new snow with freezing levels back to valley bottoms. Friday: Relatively dry and cold with freezing levels in valley bottoms.

Avalanche Summary

Three separate serious incidents occurred on Monday afternoon in the Duffey Lake and Southern Chilcotin areas, all of which had similar terrain characteristics with north through east facing steep treeline features. Two of the avalanches likely involved the mid-December persistent weakness, while the third was reported to have released on basal facets in a shallow snowpack area with a 50-75cm depth. All of the avalanches resulted in serious injury and at least two of them were human-triggered.

Snowpack Summary

Gusty winds are keeping wind slabs and cornices fresh and weak. Persistent weaknesses buried mid-December are primed for avalanches in the northern part of the region. Weak surface hoar is lurking generally down 50-70cm in sheltered treeline areas and below. In exposed treeline and alpine areas, weak facets with associated crusts are down generally 80-120cm, but wind-loading has resulted in highly variable slab thicknesses. Basal facets remain a concern in shallow rocky areas. Meanwhile in the Cascades, last weeks storm snow is generally well settled and right-side-up with mostly resistant shears on storm slab weaknesses in the top metre, but fresh wind slabs are touchy.

Problems

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.

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.