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Avalanche Forecast

Archived

Jan 11th, 2013–Jan 12th, 2013

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

Regions

Northwest Coastal.

Confidence

Good

Weather Forecast

Saturday: A mix of sun and cloud with a chance of flurries. Freezing level is at valley bottom with alpine temperatures around -6. Winds are light from the northwest. Sunday: Mainly cloudy with a chance of flurries. Freezing level remains at valley bottom with an above freezing layer developing late in the day. Winds are moderate to strong from the northwest. Monday: Mainly cloudy. Alpine temperatures should rise during the day with an above freezing layer between 1500 and 2000 m. Winds are moderate to strong from the north. 

Avalanche Summary

There are reports of isolated slab avalanches up to size 2 from wind loaded slopes in response to the northerly outflow winds. Clear weather on Wednesday revealed a previous natural avalanche cycle (+48 hours) with slabs up to size 3. Most events appeared to release within the recent storm snow, with a few events suspected to have stepped down to the late December surface hoar or facet layers.

Snowpack Summary

Northerly outflow winds have produced new wind slabs in exposed terrain, primarily near the coast. A dusting of new snow may have buried a new layer of surface hoar that formed on Wednesday night. Below this the recent storm snow is settling and gaining strength, but a weak layer of surface hoar or facetted snow sits at the base of the storm snow (down 60-90 cm). Recent snowpack tests give generally moderate sudden planar, or "pops", results on this buried surface hoar layer and indicate potential for wide propagation. Near the base of the snowpack, a crust/facet layer continues to concern local avalanche professionals. This weakness is unlikely to be triggered by a single person, but it remains possible with a very heavy load (e.g. cornice fall) or from a thin-spot trigger point.

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.