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Avalanche Forecast

Archived

Jan 3rd, 2021–Jan 4th, 2021

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

  

25-35 cm of new snow and strong southwesterly winds Saturday night formed widespread reactive storm slabs at all elevations. Human triggering of large storm slab avalanches continues to be likely on Monday.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

  

SUNDAY NIGHT: Mostly cloudy / Moderate, west ridgetop wind / alpine low temperature -11 / Freezing level valley bottom.

MONDAY: Cloudy with isolated flurries; 0-3 cm. / Strong, southwest ridgetop wind / alpine high temperature -6 / Freezing level 1000 m.

TUESDAY: Mostly cloudy / Moderate, southwest ridgetop wind / alpine high temperature -6 / Freezing level 1000 m.

WEDNESDAY: Cloudy / Strong, southwest ridgetop wind / alpine high temperature -5 / Freezing level 1200 m.

Avalanche Summary

Several natural and skier triggered storm slab avalanches up to size 2 were reported on Saturday.

On Thursday, a ski cut resulted in a size 2 persistent slab avalanche on a northeast aspect in the alpine near Kicking Horse Mountain Resort. MIN report HERE.

A skier triggered avalanche was reported in the Golden area on Wednesday. Check out the MIN report HERE. 

These recent avalanches are a reminder that when persistent slabs are the problem; conservative terrain choices are the answer.

Snowpack Summary

25-35 cm. of new snow, strong southwest winds and mild temperatures have formed widespread reactive storm slabs at all elevations.

There are currently several layers of concern in much of this region's snowpack. The recent 40-50 cm of snow has buried yet another layer weak layer of surface hoar that was reported in the golden area. The mid December surface hoar is down 90-130 cm. Although there have been no new reports of avalanches on this layer in the last few days, it remains possible to human 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 sitting 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

  • Uncertainty is best managed through conservative terrain choices at this time.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
  • Remote triggering is a concern, watch out for adjacent and overhead slopes.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.