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Avalanche Forecast

Archived

Feb 20th, 2017–Feb 21st, 2017

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

Regions

South Rockies.

Forecast new snow and wind will elevate the avalanche danger on Tuesday.

Confidence

Moderate - Intensity of incoming weather systems is uncertain on Tuesday

Weather Forecast

Tonight: 5-8 cm of new snow combined with strong southwest winds and overnight freezing down to valley bottoms. Tuesday: 3-5 cm of new snow with moderate westerly winds and daytime freezing up to 1500 metres. Wednesday: Chance of flurries with moderate southwest winds and alpine temperatures around -8. Thursday: 3-5 cm of new snow with light northeast winds and alpine temperatures around -15.

Avalanche Summary

Forecast new snow and wind may develop new storm slabs at treeline and above. These new storm slabs may not bond well to the old surface crust. Also keep in mind that the deep persistent slab problem is a low probability/high consequence scenario that warrants extra caution around large open slopes, especially in shallow snowpack areas.

Snowpack Summary

Forecast new snow and wind may develop new storm slabs. These new storm slabs may add to the recent snow that sits above a thick rain crust below 1900 m. A stiff midpack sits above weak sugary snow near the ground. This deep persistent weakness is primarily a concern in shallow snowpack areas. Watch this video from the South Rockies field team for some recent test results on this layer.

Problems

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.

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.