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Avalanche Forecast

Archived

Feb 27th, 2013–Feb 28th, 2013

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

South Coast.

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain on Thursday

Weather Forecast

A very wet flow (Pineapple Express) is forecast, but exactly when and where the intense precipitation will occur is a matter of great uncertainty.  Thursday-Saturday: Moderate to heavy precipitation. Strong to extreme SW winds. Freezing level around 1600 m, rising for a time to 2000 m.

Avalanche Summary

Numerous skier-triggered slabs have been triggered remotely, propagating across surprising distances and generally surprising people at all elevations. Details of some of these recent incidents can be found here. A natural cycle to size 2.5 occurred on Sunday night and Monday in response to new snow and wind-loading. Expect more avalanche activity over the next few days.

Snowpack Summary

Two very touchy weaknesses of surface hoar and/or a crust within the upper metre or so of the snowpack have already been responsible for a number of avalanche incidents. Add an intense storm, with heavy precipitation rates, warming and very strong winds, and we have a good recipe for widespread avalanche activity. The lower snowpack is well settled.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.