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Avalanche Forecast

Archived

Dec 3rd, 2012–Dec 4th, 2012

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

Regions

South Columbia.

Confidence

Poor - Due to limited field observations

Weather Forecast

Synopsis: A frontal system will move through southern BC on Tuesday bringing moderate snow, very strong winds, and rising freezing levels. Unsettled and cooler conditions are expected in the wake of this system.  Tuesday: Moderate snow – 15-20 cm; the freezing level could jump to 1500 m; winds are very strong from the southwest. Wednesday and Thursday: Cloudy with flurries; the freezing level lowers to near valley bottom.

Avalanche Summary

Several natural avalanches up to size 2.5, and skier controlled avalanches up to size 2 were reported over the weekend. A natural avalanche cycle was observed primarily on Saturday. Expect avalanche activity to increase again on Tuesday with forecast wind and snow.

Snowpack Summary

Up to 70 cm of moist storm snow has fallen in the past several days. This snowfall was accompanied by generally moderate south-southwest winds, forming wind slabs in exposed leeward terrain. Below the storm snow may be a layer of surface hoar or a thin crust. There are no new snowpack tests on this layer and recent reports describe the surface hoar as being small and spotty.Deeper in the snowpack you might find a second thin 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. Recent snowpack tests give occasional hard sudden collapse (Drops) results on the early November layer. There is potential for this layer to wake up with continued loading from snow and wind, or for storm slabs to "step down" creating a very large and destructive avalanche.

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.