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Avalanche Forecast

Archived

Nov 30th, 2012–Dec 1st, 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 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

Sea To Sky.

Confidence

Poor - Timing, track, or intensity of incoming weather is uncertain 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 the forecast period. Saturday: FLVL’s 1200 m, snow amounts 10-15 cm, ridgetop winds SE 40-50 km/hr, alpine temps near -4.Sunday: FLVL’s 1200m, snow amounts 5-10 cm, ridgetop winds S 10 km/hr, alpine temps -4.Monday: FLVL’s 1100 – 1400m, snow amounts 5-10 cm ridgetop winds S 35 km/hr, alpine temps -5.

Avalanche Summary

Explosive testing produced numerous size 1-1.5 slab avalanches on NW-N aspects. All instabilities reacting within the storm snow.

Snowpack Summary

The region will continue to see moderate amounts of new snow, and strong SW winds. Storm slabs and fresh wind slabs will load a variety of weak surfaces. These (now buried) surfaces consist of large surface hoar, a thin sun crust, and surface facets. Below this, the mid-pack seems to be fairly settled, strong and bridging instabilities that may exist deeper.Under the mid-pack (90-150 cm down) sits the early November facet/ crust persistent weakness. Recent snowpack tests have shown sudden collapse (or "drops") results on the early November facet/crust deep persistent weakness, but 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.). Areas that are most susceptible to trigger this deep persistent weakness are shallow, thin and variable snowpack deposition spots.To view a recent snow pit profile from the Spearhead Range, check out the Wayne Flann Avalanche Blog.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.