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Avalanche Forecast

Archived

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

Regions

Cariboos.

Confidence

Poor - Due to limited field observations for the entire period

Weather Forecast

An upper level trough sitting offshore will influence a strong SW, moist onshore flow with a series of embedded systems. As the trailing cold front passes through the interior, freezing levels will fall and snow amounts will be in the light-moderate ranges.  Freezing levels will remain near valley bottom for the forecast period.Wednesday: Snow amounts 5-10 cm, ridge top winds W 60km/hr, alpine temps near -11.Thursday: Snow amounts near 10 cm, ridge top winds SW 25 Km/hr, alpine temps near -9.Friday: Snow amounts near 10 cm, ridge top winds S 10 km/hr, and alpine temps near -12.

Avalanche Summary

There are limited recent observations; however, I suspect natural avalanche activity will  increase into Wednesday with forecast snowfall and  strong winds.

Snowpack Summary

New storm snow 30-50 cm over the past 3 days blankets the region. Instabilities (surface hoar layer, and a thin sun crust) may exist within or down 40-60 cm. We have very limited information on the extent or sensitivity of these layers in this region. A second buried surface hoar layer, down about 115 cm, and the early November rain crust (facet-crust combo), over 140cm down in some locations, remain a concern for isolated deep slab avalanches. Average snow depths at treeline seem to be between 140cm and 180cm. Elevations below 1500m are still reported as below threshold. In general, snowpack data is sparse in this region and significant variations likely exist from one drainage to another. 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.