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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 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 Columbia.

Confidence

Poor - Due to limited field observations

Weather Forecast

Synopsis: A broad and persistent trough of low pressure of the coast of BC will maintain a westerly-southwesterly flow with mild and wet conditions for the next few days. A strong frontal system should move across southern BC on Tuesday bringing heavier precipitation and rising freezing levels. Monday: Light to moderate snowfall – 10-15 cm; the freezing level is around 1000 m; winds are light to moderate from the southwest. Tuesday: Heavy snow – 25-35 cm; the freezing level could jump to 1600 m; winds are strong from the southwest. Wednesday: Cloudy with flurries; the freezing level lowers to near valley bottom.

Avalanche Summary

A widespread natural avalanche cycle was reported in parts of the region on Saturday. Avalanches up to size 2 were observed, mainly involving the recent storm snow and likely failing on the late November surface hoar layer.

Snowpack Summary

Up to 70 cm of moist storm snow has fallen in the past 3 days. This snowfall was accompanied by generally moderate southerly winds, forming wind slabs in exposed leeward terrain. Below the storm snow is a layer of surface hoar or a thin crust. There are no new snowpack tests on this layer, but it is likely that this layer is primed for natural and skier triggered avalanches.Deeper in the snowpack you might find a thin, spotty surface hoar layer about 100cm down. As well, the early November rain crust now sits over 120cm down in most locations (at treeline and above) and may exist in combination with facets. These layers seem to have been unreactive in recent days, but may have the potential to 'wake-up' with continued loading and forecast warming. There is also the potential for storm slabs to "step down" creating a very large and destructive avalanche.

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.