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Avalanche Forecast

Archived

Dec 7th, 2013–Dec 8th, 2013

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

Purcells.

Confidence

Poor - Due to the number of field observations

Weather Forecast

The dominating arctic ridge continues, bringing cold and dry conditions through the forecast period.Sunday: Mainly sunny with cloudy periods. Alpine temperatures are showing a high of -20. Light ridgetop winds from the NW.Monday: Mix of sun and cloud. Alpine temperatures are showing a high of -15. Ridgetop winds strong from the West. Tuesday: A mix of sun and cloud. Alpine temperatures are showing a balmy -13. Ridgetop winds are light from the East.

Avalanche Summary

No recent avalanche activity to report.

Snowpack Summary

Snowpack depths at treeline vary across the region, averaging 70-110 cm. In the Southern part of the region there is 40-70cm of new snow over the late-November surface hoar/ crust/ facet interface that may be reactive, especially in sheltered northerly aspects where the surface hoar is better preserved.In the northern part of the region the lower/mid snowpack is fundamentally weak, composed of an early season crust (more prevalent on north aspects) and weak faceted crystals above and below the crust. This may be reactive from thin spot triggers, or larger triggers (sledder getting air time and dropping onto the suspect slope below). Strong NE winds after the storm have caused reverse loading and wind slab formation on SE through W aspects on open slopes and behind terrain features.While many areas did not receive enough new snow to create a new slab problem on top of these weak layers, there are likely areas where a persistent slab does exist.

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.

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.