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Avalanche Forecast

Archived

Jan 26th, 2019–Jan 27th, 2019

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

Regions

Purcells.

Avoid large terrain features such as alpine bowls and steep lines down from ridges where there is a chance of being caught in a very large avalanche. Updated Purcell Forecaster Blog here.

Confidence

Moderate -

Weather Forecast

Sunday marks the start of a pronounced ridge of high pressure that is expected to be with us through at least Tuesday. This period is marked by mostly clear skies, cooler temperatures and a lack of precipitation.SATURDAY NIGHT: Freezing level at valley bottom, light west/southwest wind at most elevations, extreme northwest wind at ridgetop, no precipitation expected.SUNDAY: A few clouds, freezing level beginning at valley bottom rising to around 1000 m during the day, moderate to strong northwest wind, no significant precipitation expected.MONDAY: Mostly clear skies, freezing level at valley bottom, light northwest wind, no precipitation expected.TUESDAY: Clear skies, freezing level at valley bottom, light variable wind, no precipitation expected.

Avalanche Summary

On Friday wind slab avalanches up to size 2 were reported from east and northeast aspects between 2000 and 2400 m.One skier-triggered avalanche was reported on Wednesday in storm snow at approximately 2000 m that released 40 cm below the surface. On Thursday, explosive control work released another slide on the deep persistent layer at the base of the snowpack. There is a MIN report from last Saturday that shows a natural avalanche (size 3.5) in International Basin, also on the deep persistent layer. Check out the MIN here. Dealing with the deep persistent basal facet/crust problem requires avoiding terrain where this kind of avalanche is possible.

Snowpack Summary

Up to 20 cm of recent snow has buried large surface hoar crystals which, on southern aspects, may rest on a sun crust. In most places, there is still insufficient snow over this layer to create a widespread problem. However, locally, in deeper snowpack areas, or where the wind has blown snow above this layer, avalanches large enough to be of concern could be triggered. The snowpack also has a deeply buried weak layer near the ground composed of weak faceted grains and a crust that is present in most of the region. There have been sporadic reports of people triggering this layer in areas where the snowpack is shallow. The most likely trigger points include ridgelines, large open slopes and bowls in the alpine, particularly those that have rocky or variable (thin to thick) features. If you trigger a deep persistent slab it will go big and be a highly destructive avalanche.

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.

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.