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Avalanche Forecast

Archived

Dec 10th, 2021–Dec 11th, 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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Purcells.

Today is a good day to choose mellow slopes that are protected from the wind. Time will tell how well the new snow bonds to the wind slabs and crust that it covered. 

Confidence

Moderate - We are confident the likelihood of avalanche will increase with the arrival of the forecast weather.

Weather Forecast

FRIDAY NIGHT: Mostly cloudy. 5-10 cm of snow expected. Strong southwest wind. Alpine low around -13.

SATURDAY: Overcast. 10-20 cm of snow expected. Possibly another 10 cm overnight. Strong to extreme southwest winds. Expect wind speed to increase drastically as you gain elevation. Freezing levels climb to between 1000 and 1500m. Alpine highs of -3. 

SUNDAY: Mostly cloudy. 0-7 cm snow expected. Moderate to strong southwest wind. Freezing levels below 1000m. Alpine highs of -6. 

MONDAY: Mostly cloudy. 0-5 cm snow expected. Light to moderate south winds. Warming through the day, alpine high around -7.

Avalanche Summary

No new avalanches observed. Expect human triggered avalanches to become likely as the storm snow accumulates.

On Wednesday, natural and skier triggered slab avalanches were observed at treeline and above to size 1.5.

Explosive control work near Golden on 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 Dec 3 in Quartz Creek also reported deep persistent avalanches failing at the base of the snowpack. 

While these observations are almost a week old, this deeply buried weak layer is still a concern.

Snowpack Summary

Over the course of the day, 15-25 cm of new snow that is falling with strong wind and warming temperatures has the potential to create a reactive, upside-down snowpack. 

The new storm snow is falling on 50cm of settling snow from the last storm. This overlies a thick and supportive melt freeze crust on all aspects up to 2400m. Westerly winds have redistributed new snow into deeper deposits in wind loaded features at higher elevations.

A late October facet/crust layer of concern sits at the bottom of the snowpack above 1900m. This layer has been reactive to human triggers, producing large avalanches. This layer is widespread 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

  • Watch for fresh storm slabs building throughout the day.
  • Be aware of highly variable recent wind loading patterns.
  • Be mindful that deep instabilities are still present and have produced recent large avalanches.

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.

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.