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Avalanche Forecast

Archived

Dec 28th, 2018–Dec 29th, 2018

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

South Rockies.

Extreme winds will redistribute any and all loose snow. Expect to see scouring, hard wind slabs, and snow transport. Keep the persistent weak layer in mind, it may be easier to trigger in areas affected by wind.

Confidence

Low - Due to the number of field observations

Weather Forecast

FRIDAY NIGHT: Cloudy with isolated flurries, up to 5 cm accumulation. Moderate west wind. Alpine low of -13C.SATURDAY: Cloudy with scattered flurries, trace to 10 cm accumulation. Moderate west wind gusting strong to extreme. Alpine high -4, freezing level rising about 1500 m. Environment Canada has issued a wind warning for the area around Crowsnest Pass and the front ranges here.SUNDAY: Mix of sun and cloud. Light northwest wind with occasional moderate-strong gusts. Alpine high -6C.MONDAY: Mix of sun and cloud. Light northwest wind with occasional moderate gusts. Alpine low -16C.

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.Over the last weekend, the persistent weak layer was active, explosives triggered avalanches to size 2.5 and a cornice triggered a size 2 avalanche. Skier traffic was also able to trigger wind slab avalanches to size 2. Though avalanche activity on this layer has slowed, avalanches failing on this layer have the potential to be large and destructive.

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. Though avalanche activity on this layer has slowed down in recent days, it may still be easy for humans to trigger avalanches on this layer in certain terrain features. Steep features where the underlying ground cover is smooth, places where the snowpack depths are variable, and large convex features are some of the more likely places to trigger this layer.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

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.