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Avalanche Forecast

Archived

Nov 25th, 2012–Nov 26th, 2012

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

Regions

Cariboos.

This bulletin is based on limited data. Local variations in conditions are likely to exist. Check out the forecasters blog for further details on interpreting early season bulletins.

Confidence

Poor - Due to limited field observations

Weather Forecast

Skies will be mostly clear for Monday with increasing cloud on Tuesday and a chance of light flurries on Wednesday. Ridgetop winds should be mostly light from the west/northwest switching to light from the southeast with the approach of Wednesday's system. Freezing levels should climb gradually from 700m on Monday to 1100m by Wednesday.

Avalanche Summary

Just before the weekend we received a report from the Valemount area of  a snowmobile triggering a size 2.0 avalanche that was about 70 cm deep and about 80 metres wide. The avalanche was triggered from a shallow weak area, and suspect that the weak layer was either the November crust or buried surface hoar. Any field observations are welcome at [email protected].

Snowpack Summary

Some parts of the region received over 30cms of new snow on Thursday adding to the healthy amounts that fell throughout the week. Although alpine wind data has been sparse, velocities in neighboring regions have been in the upper end of moderate. That said, I'd be highly curious about the possibility of windslabs in exposed areas. Although storm slab reactivity is still possible, a break in the snowfall over the weekend has most likely given the upper snowpack a chance to settle and gain some strength.  There may be a thin buried surface hoar layer down about 85 cm in the alpine. As well, the November rain crust now exists over 100cm down in some locations and may exist in combination with facets. This layer has shown sudden planar test results.

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.