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Avalanche Forecast

Archived

Dec 20th, 2013–Dec 21st, 2013

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

Regions

Purcells.

Confidence

Fair - Wind effect is extremely variable

Weather Forecast

Saturday: Mainly cloudy with a chance of flurries and sunny breaks. Little precipitation expected,  freezing level remains at valley bottom and moderate gusty northwest winds continue. Sunday: A mix of sun and cloud. The freezing level is near valley bottom and the upper flow continues to be northwesterly. Monday:  The tail end of a Pacific frontal system will move through the southern part of the Province, bringing light to locally moderate precipitation.

Avalanche Summary

One size 3 accidentally triggered slab avalanche was reported near Golden on Wednesday. This slide was triggered by a skier on a north-northeast aspect in the alpine and likely released on a persistent weakness near the bottom of the snowpack. The initial slide also sympathetically triggered another size 2.5 lower down the slope. Fortunately no one was buried or injured. Several other natural and explosive triggered avalanches (size 1.5-3) have been recently reported . This type of avalanche activity may be a good indication of the potential for large avalanches during periods of loading.

Snowpack Summary

Continued accumulation of low density new snow from the latest systems, accompanied by moderate W-NW ridgetop winds. Expect to find dense wind slabs in exposed lee terrain at and above treeline. A couple of notable persistent weak layers can be found in the top 60 cm. These layers have produced variable results with snowpack tests, but are increasingly concerning as the load above increases and/or a slab develops.  Snowpack depths vary widely across the Purcells from North to South.  If you're in the Golden area check out the latest update on local conditions from Skiing Golden. At the base of the snowpack are weak facets and depth hoar combined with a crust from early October. This deep persistent weakness may be stubborn to trigger, especially in deeper snowpack areas, but the sensitivity to triggers likely increases in shallower locations, especially on steep, convex, north-facing slopes. Snow depth is still below threshold in many areas below treeline.

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.

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.