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Avalanche Forecast

Archived

Dec 3rd, 2012–Dec 4th, 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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Cariboos.

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 slightly rising freezing levels. Unsettled and cooler conditions are expected in the wake of this system.  Tuesday: Moderate snow – 10-20 cm; the freezing level could jump to 1000 m; winds are very strong from the southwest. Wednesday and Thursday: Cloudy with flurries; the freezing level lowers to valley bottom.

Avalanche Summary

There are limited recent observations; however, it is likely that was a natural avalanche cycle on Saturday and into Sunday. Avalanche activity should increase again on Tuesday with forecast moderate snowfall and very strong winds. We welcome all observations at [email protected].

Snowpack Summary

Instabilities may exist within or under the recent storm snow. A surface hoar layer or thin crust may be found at the base of the storm snow, down 40-60 cm, but we have very limited information on the extent or sensitivity of this layer in this region. A second buried surface hoar layer, down about 115 cm, and the early November rain crust (facet-crust combo), over 125cm down in some locations, remain a concern for isolated deep slab avalanches. Average snow depths at treeline seem to be between 140cm and 170cm. 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.