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Avalanche Forecast

Archived

Dec 21st, 2012–Dec 22nd, 2012

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

Regions

Northwest Coastal.

Confidence

Fair - Due to limited field observations

Weather Forecast

Saturday: Mostly clear skies / Moderate southeast winds / Temperature inversion with ridgetop temperature of -12.0Sunday: Mostly clear skies with trace amounts of new snow / Moderate southeast winds / Temperature inversion with ridgetop temperature of -13.0Monday: Trace amounts of new snow / Light southeast winds / Ridgetop temperature of -16.0

Avalanche Summary

An explosives controlled size 2 cornice fall/ windslab was reported from the region on Thursday. No other avalanches have been reported.

Snowpack Summary

Light amounts of new snow have been redistributed by winds at higher elevations. This overlies the past week's storm snow which has most likely settled and gained significant strength. A buried surface hoar layer, reported to be 5 to 10mm thick, has produced sudden snowpack test results down about 80cm in the Shames backcountry, and may exist in other areas too. Avalanche professionals continue to monitor a faceted crust near the ground which has been reactive this week in the Bear Pass area. It seems this problem is confined to alpine areas and likely needs a large trigger and/or a shallow snow pack feature to trigger. Cornices are also really big and forecast strong winds and cooling temperatures could make them especially heavy and brittle.

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.

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.