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Avalanche Forecast

Archived

Jan 10th, 2012–Jan 11th, 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.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

Sea To Sky.

Confidence

Good - -1

Weather Forecast

A ridge of high pressure will keep the region dry and sunny for Wednesday, Thursday and Friday. Winds will be light and variable throughout. There is a pulse of warm air encroaching into the region from the coast. This may cause an above-freezing level layer to form from 1800-2200m on Wednesday and it's possible this will persist into Thursday and Friday.

Avalanche Summary

There were reports of two skier-triggered avalanches near Whistler that went on the recent storm snow interface down around 60 cm, one from Monday and one from Tuesday. Both were size 2 and released on a NE aspect around 2000 m. The event on Tuesday is a good reminder that the storm slab instability can stay reactive for some time after the end of the storm. There have been no recent reports of activity stepping down to any of the lower weak layers in the snowpack.

Snowpack Summary

At treeline, snowpack depths are around 260cm.The upper snowpack comprises a series of storm snow layers, which have generally bonded well to each other and are now gaining strength. Rain to approximately 2000 m from the last storm that has now refrozen has left us with a crust buried by a skiff of snow. In the alpine, above the elevation where rain fell, fresh new wind slabs have developed in response to very strong winds. Expect winds to shift from southwesterly to northerly, potentially creating some localized reverse loading. Concern for lower snowpack layers remains only in shallow snowpack areas. Facets associated with a crust from mid-December and/or sugary facets at the base of the snowpack could be a concern in areas you know to be unusually shallow, or where you can see rocks poking up out of the snow.

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.