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Avalanche Forecast

Archived

Jan 5th, 2012–Jan 6th, 2012

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

Regions

South Coast.

Confidence

Good - -1

Weather Forecast

Friday: Dry with increasing cloud cover and flurries possible in the evening. Freezing levels in valley bottoms and light winds. Saturday: Cloudy but dry with moderate precipitation starting in the evening. Freezing levels are expected to rise to 1300m and southwesterly winds increase to moderate with the onset of precipitation. Sunday: Isolated moderate snow flurries with strong southwesterly winds.

Avalanche Summary

Widespread natural avalanche activity up to Size 3 was reported on Wednesday. Fresh storm and wind slabs, as well as deeply buried persistent slabs remain sensitive to human triggers.

Snowpack Summary

Weaknesses within and under the 60-100+cm of storm snow will need some time to settle and strengthen. Persistent weaknesses remain a concern in the northern part of the region. Buried surface hoar on sheltered treeline slopes and below and facets with associated crusts in exposed treeline and alpine areas are probably down well over a metre in most places, and facets lurk near the base of the snowpack in shallow rocky areas. Wind-loading has resulted in highly variable slab thicknesses with the potential for fractures triggered in highly sensitive thin slab areas to propagate into highly destructive deep slab avalanches. Furthermore, weaknesses within the slab create the potential for step-down fractures.

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.

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.

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.