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Avalanche Forecast

Archived

Dec 19th, 2013–Dec 20th, 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

Weather Forecast

Friday: Cloudy with light to moderate snowfall around 5 cm. The freezing level is at valley bottom and ridgetop winds are light to moderate from the northwest. Saturday: Mainly cloudy with a chance of flurries and sunny breaks. The 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.

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 1.5-2.5) were reported - most were from the northern part of the region where up to 20 cm of new snow fell in the previous 24 hours. This type of avalanche activity may be a good indication of the potential for large avalanches during periods of loading.

Snowpack Summary

Up to 20 cm of low density new snow fell with the latest system, accompanied by moderate W-NW ridgetop winds. Expect to find dense wind slabs in exposed lee terrain at and above treeline. A couple 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. 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.