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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.

Regions

Kootenay Boundary.

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 1600-1800 m; winds are very strong from the southwest. Wednesday and Thursday: Cloudy with flurries; the freezing level lowers to 600-800 m. 

Avalanche Summary

Several natural and skier triggered slab avalanches up to size 2 were reported throughout the region on the weekend. Most of these avalanches were 40-50cm deep and involved the recent storm snow. Check out the Incident Report database for a couple recent submissions. I expect much of the same for Tuesday with forecast snow, strong winds, and warming.

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 is a layer of surface hoar or a thin crust. Recent snowpack tests give consistent easy results on this layer.In the mid snowpack, there may be a thin buried surface hoar layer between 80 and 100cm deep. At the base of the snowpack sits the early November rain crust. This layer seems most likely to be found in deeper snowpack areas at higher elevations. These layers have been unreactive in recent days, but may have the potential to 'wake-up' with continued loading and forecast warming.In general, snowpack data is sparse in this region and significant variations likely exist from one drainage to another. In short, digging down and making your own observations will be critical to safe slope selection. Any observations from the field are welcome at [email protected].

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.