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

Regions

Northwest Inland.

Confidence

Poor - Due to limited field observations

Weather Forecast

Saturday: Mostly clear skies / Moderate southeast winds / Temperature inversion with ridgetop temperature of -14.0Sunday: Mostly clear skies with trace amounts of new snow / Moderate southeast winds / Temperature inversion with ridgetop temperature of -14.0Monday: Trace amounts of new snow / Light southeast winds / Ridgetop temperature of -17.0

Avalanche Summary

No recent avalanches have been reported.

Snowpack Summary

Light amounts of new snow overlie older storm and windslabs which have likely settled and gained strength. It is suspected that the recent light accumulations have been redistributed into wind slabs in some areas.Spotty surface hoar was buried in the upper snowpack in sheltered treeline areas although little is known about its reactivity. Of concern is a November facet/crust layer which can be found near the base of the snowpack. This layer, which seems widespread, is possibly gaining some strength. Having said that, it may be triggered from thin-spot trigger points, or with a heavy load and has the potential for large, destructive avalanches. In general the snowpack depths, and therefore strength is highly variable due to windy conditions this season.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.