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Avalanche Forecast

Archived

Mar 6th, 2013–Mar 7th, 2013

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

Sea To Sky.

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Thursday: Trace amounts of new snow / Light northwest winds / Freezing level at 1200mFriday: Mix of sun and cloud / Light north winds / Freezing level at 1500mSaturday: Clear skies / Light northwest winds / Freezing level at 1400m

Avalanche Summary

Explosives control continued to produce results up to size 3 on Sunday. There were a couple reports of skier triggered avalanches up to size 2 on Monday, primarily from northeast through southeast aspects in the alpine.

Snowpack Summary

The snow surface consists of surface hoar, a sun crust, faceted snow, or thin soft wind slabs depending on aspect and elevation. Below this the recent storm snow (70-120 cm) continues to settle and strengthen. Snowpack tests are still giving generally moderate shears at various density changes within the storm snow, but triggering these instabilities has become more difficult. A weakness of surface hoar and/or a crust exists near the base of the storm snow (now 1-2 m deep). This layer was the culprit in most of the large avalanches that occurred last weekend. This layer could still be triggered in shallow rocky areas or by large triggers like a cornice fall. I would suggest avoiding any large slope that did not release during the latest avalanche cycle. Below this weakness the snowpack is strong and well settled.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.