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Avalanche Forecast

Archived

Jan 7th, 2021–Jan 8th, 2021

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

Regions

Purcells.

The snowpack is complex and the potential exists to trigger persistent slab avalanches. While these avalanches are becoming less likely, the consequences are high. The uncertainty associated with complex snowpacks is best managed with conservative terrain choices.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

THURSDAY NIGHT - Mainly cloudy / light to moderate southwest wind / alpine low temperature near -7 

FRIDAY - A mix of sun and cloud / light to moderate southeast wind / alpine high temperature near -5 

SATURDAY - Mainly sunny / light south wind / alpine high temperature near -8 

SUNDAY - A mix of sun and cloud / light to moderate west wind / alpine high temperature near -7

Avalanche Summary

On Wednesday, there were a few size 1 human triggered wind slab avalanches reported in the region.

On Tuesday, there was a human triggered size 2.5 avalanche reported on an east aspect at treeline in the Lower Holt area, near Golden. Two people were caught in this avalanche but were luckily uninjured. For a full report of this incident, click here.

There was another human triggered avalanche reported in the region on Tuesday on a northeast aspect at treeline near Glacier National Park. The MIN report can be viewed here.

There were a few reports of natural and explosives triggered size 2-2.5 wind and storm slab avalanches on Monday.

On Sunday there were reports of numerous natural, human and explosives triggered avalanches up to size 2. There was also one natural size 2.5 deep persistent slab avalanche reported on a north aspect at 2500 m near Invermere. 

A notable avalanche incident occurred on Sunday and can be viewed here.

Snowpack Summary

Recent fresh snow with strong southerly wind has likely formed wind slabs in leeward terrain features at upper elevations.

There are currently several layers of concern in much of the region's snowpack. 40-60 cm of snow sits on a weak layer of surface hoar that was reported in the Golden area. 

The mid-December surface hoar is now down 90-140 cm. Although there have been no new reports of avalanches on this layer in the last few days, it remains possible to trigger where it is well preserved. There may also be a crust near, or instead of this layer in some areas.

The lower snowpack is characterized by more crusts, the most notable is a rain crust from early November that is near the base of the snowpack, surrounded by a weak layer of sugary facets. It is most likely to be reactive to human triggers in steep, shallow, rocky areas with a thin to thick snowpack.

Terrain and Travel

  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • Uncertainty is best managed through conservative terrain choices at this time.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.