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Avalanche Forecast

Archived

Dec 29th, 2018–Dec 30th, 2018

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

Regions

South Rockies.

Lots of recent wind has redistributed snow in exposed areas and has likely set up wind slabs that could be reactive to the weight of a rider.

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

SATURDAY NIGHT: 5-10 cm additional new snow expected. Strong southwesterly winds.SUNDAY: Light snow, 2-4 cm. Moderate northwesterly winds. Treeline temperatures around -6C.MONDAY: Dry with sunny breaks. Light northerly winds. Treeline temperatures around -14C.TUESDAY: Dry with sunny breaks. Light southwesterly winds. Treeline temperatures around -15C.

Avalanche Summary

On Thursday and Friday, the South Rockies field team found weak faceted snow, saw shooting cracks and experienced whumpfing as they traveled around the Nordstrom area south of Elkford and around the Crowsnest Pass.A great MIN report from Corbin on Thursday identifies a few slabs initiating in thin, rocky areas on a south aspect. While this is in the Lizard Range and Flathead forecast region, similar conditions should be expected around the South Rockies. Check out the report here.

Snowpack Summary

The upper snowpack consists of hard wind slabs on north aspects, scoured and a shallower snowpack on south aspects, and a mixed bag of lower density snow in more sheltered areas. In total, 60-90 cm of December snow has formed a slab that sits on a persistent weak layer of facets (sugary snow) that formed during the dry weather in early December. This layer is most likely to be triggered on steep features where the underlying ground cover is smooth, areas where the snowpack depths are variable, or on large convex features.The lower snowpack has a weak structure composed primarily of facets over a crust on the ground. It is very likely that an avalanche triggered on the persistent slab would step down to the lower facets, resulting in a full depth avalanche.

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.