Dashboard Regions Weather Stations Radar Alerts Glossary
Contact About
Log In

Register for an account and never miss a forecast again!

Register

Avalanche Forecast

Archived

Dec 7th, 2021–Dec 8th, 2021

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

Purcells.

Expect fresh wind slabs at ridge crest and in cross loaded terrain. Keep your head up - variable winds may have loaded unexpected features. 

Deeper weak layers are still possible to trigger, stay away from large unsupported slopes and rocky start zones. 

Confidence

Moderate - Uncertainty is due to the complexity of the snowpack’s structure. Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

A front brings light snow and strong winds overnight. Wednesday afternoon will see clearing skies and calmer conditions as the front moves out, replaced by a weak high pressure system.

TUESDAY NIGHT: Snow beginning late evening with up to 5cm expected by Wednesday morning. Moderate to strong southwest winds. Freezing level valley bottom.

WEDNESDAY: 5-15cm over the day with strong westerly winds. Freezing level below 1000m, alpine highs of -8.

THURSDAY: Cloudy with up to 4cm of snow over the day. Winds ease to moderate westerlies. Freezing levels at valley bottom. Alpine highs of -8. 

FRIDAY: Chance of flurries with moderate westerlies. Freezing level at valley bottom and alpine highs of -8.

Avalanche Summary

Explosive control work near Golden on Sunday Dec 5th produced a size 2 slab avalanche that failed to ground in a steep and unsupported terrain feature. A naturally triggered size 3 was also observed on a west facing slope in the Northern zone of the Purcells, believed to have occurred around the 2nd of December. 

Two Mountain Information Network (MIN) reports (MIN 1 and MIN 2) from Friday, Dec 3 in Quartz Creek report deep persistent avalanches failing at the base of the snowpack. 

A MIN report submitted on Sunday Dec 5 from the Brewer Creek area reported a column test failure on the Nov 21 SH down 60cm. Several avalanches that occurred in the Toby Creek drainage are thought to have failed on the same layer. This is believed to be lurking around the Toby Creek drainage area, however data is sparse this early in the season and this layer is believed to extend to other areas.

Snowpack Summary

20-50cm of low density snow sits over a supportive crust up to 2400m on all aspects. In the high alpine, storm snow sits on a variety of wind affected surfaces.

Westerly winds have redistributed new snow into deeper deposits in wind loaded features at higher elevations.

A surface hoar layer extends throughout the Toby Creek drainage and surrounding areas - down 30 to 70 cm in sheltered features at treeline and below. Recent snowpack tests have shown this layer to produce sudden propagating fractures. We have limited knowledge of the distribution of this layer, but suspect is its most prevalent between 1900-2400m.  

A late October facet/crust layer of concern sits at the bottom of the snowpack above 1900m. This layer has been reactive to human and explosive triggers, producing large avalanches. This layer is widespread throughout the region and will likely continue to be a layer of concern.

Average snowpack depth at treeline is 100-180cm, with the deepest snowpack found near the Bugaboos. 

Terrain and Travel

  • Be aware of highly variable recent wind loading patterns.
  • Avoid slopes that sound hollow or drum-like.
  • Avoid areas with a thin or variable snowpack.

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.