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Avalanche Forecast

Archived

Dec 2nd, 2012–Dec 3rd, 2012

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

Regions

South Coast.

Confidence

Poor - Due to limited field observations for the entire period

Weather Forecast

A broad upper trough remains just offshore while a cooler, unstable onshore flow will persist and strengthen through Monday. On Tuesday an embedded frontal system will bring heavy amounts of precipitation, rising freezing levels and strong SW winds hammering the region. Wednesday the flow will switch from SW to NW, and precipitation amounts will ease up.Monday: Fzlvl’s 1000 m, snow amounts 5-10 cm, ridgetop winds S 30, alpine temps -6.Tuesday: Fzlvl’s 1700 m in am falling to 700 m, snow amounts 15-20 cm, ridgetop winds SW 30-gusting to 70 km/hr, alpine temps -4.Wednesday: Fzlv l’s 700 m, snow amounts near 5 cm, ridgetop winds S 30 km/hr, alpine temps -9.

Avalanche Summary

No new avalanche observations have been reported. With strong winds and heavy precipitation forecast for Tuesday, expect avalanche danger to be on the rise with natural avalanche activity likely.

Snowpack Summary

Storm slabs and new wind slabs will load a variety of weak surfaces and be touchy. These surfaces consist of large surface hoar, a thin sun crust, surface facets. The new snow may have a poor bond to these underlying weaknesses. Below the surface, the mid-pack seems to be settled and bridging over the early Nov facet/crust. However, near the bottom of the snowpack under the crust exists large, low density faceted crystals. The storm (loading) on Tuesday will provide a good test on this basal weakness.Snowpack tests from earlier this week showed sudden collapse results on the early November facet/crust deep persistent weakness. Because this weakness is so close to the ground in most areas, associated avalanche activity will likely be limited to slopes with smooth ground cover (e.g. scree slopes, rock slabs, summer firn, glaciers, etc.). Be aware of triggering this layer from thin, rocky areas, this persistent weakness my be a low probability/ high consequence scenario.

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.