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Avalanche Forecast

Archived

Dec 23rd, 2011–Dec 24th, 2011

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

Regions

Purcells.

Confidence

Fair - Due to variable snopack conditions

Weather Forecast

Saturday: Mostly cloudy with a chance of flurries. Expect moderate southwest winds and temperatures reaching -3. Due to the nature of the weather pattern, expect more precipitation on the western half of the region and on west facing slopes. Sunday: A weak cold front passes through the region giving unsettled skies with a chance of flurries. Continued southwest winds and freezing levels reaching 1100m. Monday: Expect clearing conditions under southwest winds and freezing levels to 1100m.

Avalanche Summary

No new avalanches.

Snowpack Summary

There is about 20-30cm of recent storm snow sitting over the December 12 interface of surface hoar and facets. This new snow has been deposited into soft slabs on lee features in open terrain by the consistent winds. The interface between the new snow and older surfaces is gaining strength, but still remains within the threshold of human triggering where there is sufficient load/slab properties. Some areas have a sun crust in the alpine on steep south and west aspects. Lower in the snowpack, the mid-layers are well-consolidated and strong. Near the base of the snowpack there are a few layers that have the potential to wake up with a really big storm or very heavy loads. These include a surface hoar layer from early November, a crust/facet combo from October and the interface on steep glaciated terrain with snow that did not melt over the summer.

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.