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Avalanche Forecast

Archived

Jan 3rd, 2019–Jan 4th, 2019

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

South Rockies.

The storm is loading a weak snowpack. Travel in avalanche terrain is not recommended.

Confidence

High -

Weather Forecast

THURSDAY NIGHT: Cloudy with snowfall, accumulation 10 to 20 cm, moderate to strong southwest winds, freezing level 1500 m.FRIDAY: Cloudy with snowfall, accumulation 5 to 10 cm, moderate to strong southwest winds, alpine temperature -5 C, freezing level 1400 m.SATURDAY: Mix of sun and cloud, light to moderate southwest wind, alpine temperature -5 C, freezing level 1000 m.SUNDAY: Cloudy with light snowfall, accumulation 5 to 10 cm, light to moderate southwest winds, alpine temperature -5 C, freezing level 1000 m.

Avalanche Summary

A natural avalanche cycle may be starting in the region with the substantial amount of recent snowfall. On Wednesday, a naturally-triggered large (size 3) avalanche was observed near Elkford, which likely released on Tuesday. See here. It ran full-path to valley bottom. In the far west of the region, the snowpack has been observed to be weak and touchy, as described here. New snow is loading this weak and touchy snowpack and increasing the likelihood of avalanche activity.

Snowpack Summary

Large variability in snow depths still exists in the region, ranging from practically no snow to almost 200 cm. Upwards of 30 cm of snow fell on Thursday and more is expected on Thursday night into Friday. The snow fell with strong southwest winds, moving the snow around in exposed areas. Expect the deepest deposits in lee terrain features. This snow will sit on previous hard wind slabs, a scoured and shallow snowpack on exposed southerly ridges, and soft snow in sheltered areas.A persistent weak layer of weak and sugary faceted snow that formed during dry and cold weather in early December is buried around 60 to 90 cm. This layer is most likely to be triggered on steep features where snowpack depths are variable.The lower snowpack has a weak structure composed primarily of sugary faceted snow around a crust near the ground. Should a shallower avalanche be triggered, it is likely that it would step down and scour to the ground.

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.