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Avalanche Forecast

Archived

Nov 30th, 2012–Dec 1st, 2012

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

Regions

South Coast.

Confidence

Poor - Due to limited field observations for the entire period

Weather Forecast

The deep low pressure system off the Gulf of Alaska continues to spin a moist, warm southwesterly flow over the South Coast mountains. The weather pattern will remain continuous and active through Saturday. On Sunday afternoon sunny periods may exist. Saturday: FLVL’s 1300 m, snow amounts 5-10 cm, ridgetop winds SE 40-50 km/hr, alpine temps near -5.Sunday: FLVL’s 1300m, trace of new snow, ridgetop winds S 20 km/hr, and alpine temps -4.Monday: FLVL’s 1100 – 1200m, ridgetop winds S 30 km/hr, alpine temps -6.

Avalanche Summary

No new avalanche observations have been reported.

Snowpack Summary

The region will continue to see pulses of light-moderate snow accumulations, and strong ridgetop winds. Storm slabs and new wind slabs will load a variety of weak surfaces. 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 facetted crystals.Snowpack tests from earlier this week showed sudden collapse ("drops") 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. Below treeline the snowpack generally sits below threshold.

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.