Avalanche Forecast

Archived

Dec 11th, 2012–Dec 12th, 2012

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.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

South Columbia.

Confidence

Fair

Weather Forecast

A weak ridge moving over the region should bring lighter precipitations for Wednesday and then mainly cloudy skies in the Southern part of the region and partial clearing in the Northern part. The next system is weaker and should reach the region later Thursday and deliver some light to moderate precipitations and stronger Southwesterly winds for the rest of the period. Cool temperatures (-12 C) and lighter winds are expected for Friday.

Avalanche Summary

A few small soft slabs were triggered by skiers yesterday on the storm snow. Suspect recent sluffing in steep terrain.

Snowpack Summary

20-30 cm of warmer-denser new snow from the past few days fell on a cooler-lower density storm layer possibly creating storm slabs and also burying older windslabs. The moderate to strong North West and South West winds most likely created new windslabs on leeslopes in the alpine and at treeline. The bond within the new snow with the older storm snow interface is unknown, but it still remains a concern in the alpine and at treeline on lee slopes. There has been report of multiple significant results (sudden planar) on the Late November surface hoar layer now down around 100 cm and 150 cm in snowier areas. The early November crust is still a concern and is producing more varied results from break to sudden planar. Large planar slopes with known smooth ground cover are areas to avoid in respect to this concern.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.