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Avalanche Forecast

Archived

Mar 1st, 2013–Mar 2nd, 2013

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

Regions

South Coast.

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain for the entire period

Weather Forecast

Friday night: Ongoing precipitation. Strong SW winds. Freezing level around 1800 m.Saturday: Light precipitation. Moderate SW winds. Freezing level around 1500 m.Sunday: No snow expected. Light winds. Freezing level around 900 m.Monday: Light snow. Light winds. Freezing level around 1100 m.

Avalanche Summary

Initial reports from Friday suggest a widespread natural avalanche cycle to size 3.5.Almost every day this week, skiers have triggered slabs to size 2, failing on buried surface hoar/crusts which exist at all elevations and on all aspects. Some were triggered remotely, and they exhibited wide propagation. Details of some of these 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. A natural avalanche cycle is expected over the next few days in response to intense storm loading.

Snowpack Summary

Two very touchy weaknesses of surface hoar and/or a crust within the upper 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.