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Avalanche Forecast

Archived

Jan 4th, 2012–Jan 5th, 2012

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 unlikely, human triggered possible.
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 possible, human triggered probable.

Regions

Northwest Inland.

Confidence

Fair - Due to limited field observations

Weather Forecast

A short-lived ridge of high pressure develops over the area on Thursday, bringing mostly dry weather. Freezing levels will be at valley bottom. Winds moderate from the west. On Friday, a weak frontal system will likely bring only flurries or light precipitation with moderate SW winds. On Saturday, a stronger frontal system will give moderate to heavy precipitation, with freezing levels rising to 1500 m and strong southwesterly winds.

Avalanche Summary

High winds and poor visibility have limited observations for the last few days; however, no activity has been reported to us from this region recently. I suspect you could easily trigger a pocket of wind slab on exposed lee terrain and I'd still be nervous of triggering the mid-December surface hoar layer down around 70 cm in sheltered locations.

Snowpack Summary

New snow and strong winds have set up fresh wind slabs at higher elevations, mainly on north through east aspects in exposed lee terrain--these are likely triggerable by riders on sleds or on skis. Lower down, expect a significant rain crust to exist up to approximately 1500 m. There is now approximately 80 to 120cms of storm snow sitting above a surface hoar/crust/facet layer that was buried mid-December. The increasing depth of this weak layer makes it difficult to trigger; however, I wouldn't ignore this layer yet, as it could still be triggered by large loads such as rapid loading by new snow or rain or cornice falls. It could also be triggered by riders in shallow snowpack areas or where rocks poke up near the surface. The mid- and lower snowpack layers are well consolidated and generally strong.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

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.