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Avalanche Forecast

Archived

Jan 11th, 2013–Jan 12th, 2013

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

Fair

Weather Forecast

Saturday: Mainly sunny and cool. Freezing level is at valley bottom with alpine temperatures around -12. Winds are light from the north-northwest. Sunday: A mix of sun and cloud. Freezing level remains at valley bottom. Winds are light to moderate from the north. Monday: A mix of sun and cloud. Alpine temperatures should rise during the day with an above freezing layer developing. Winds are moderate from the north. 

Avalanche Summary

There are reports of a widespread natural avalanche cycle from Tuesday night and Wednesday. Slab avalanches up to size 3 were observed, with many events occurring below treeline and failing on the early January surface hoar layer. There are also a couple reports of skier triggered avalanches up to size 2 and avalanches being triggered from a distance.

Snowpack Summary

Up to 15 cm of low density new snow sits on the previous 40-80 cm of storm snow from earlier in the week. Northerly outflow winds have produced pockets of new wind slabs in south facing terrain, and old dense wind slabs lurk below the surface on northerly aspects. A layer of surface hoar, facetted snow, and /or a crust exists at the base of the recent storm snow. Snowpack tests show that this interface is susceptible to human triggering and has the potential to propagate widely. No significant weaknesses have been reported recently below this in the mid snowpack layers. Near the base of the snowpack, a crust/facet layer exists, which is now unlikely to be triggered, except perhaps by heavy triggers in steep, shallow, rocky terrain where more facetting has taken place.

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.