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Avalanche Forecast

Archived

Nov 30th, 2021–Dec 1st, 2021

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
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.
Below Treeline
Natural avalanches unlikely.

Regions

Purcells.

Avoid all avalanche terrain during heavy snowfall and strong winds. Avalanches may run full path and small avalanches may step down to deeper layers. 

Confidence

High - We are confident the likelihood of avalanche will increase with the arrival of the forecast weather. Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

TUESDAY NIGHT: Precipitation continues overnight with 10-25mm with strong to extreme southwest winds. Freezing levels soar above 2000m. 

WEDNESDAY: Strong southwest winds with freezing levels remaining above 2000m. 10-30cm is expected over the day with accumulations favouring the Bugaboos.

THURSDAY: Skies clear over the day with flurries tapering off. Winds ease to moderate westerlies. Temperatures drop, with freezing levels falling to valley bottom in the evening. 

FRIDAY: Cold and clear with alpine highs around -8. Freezing levels stay below 1000m with light to moderate southwesterly winds.

Avalanche Summary

Monday November 29th saw multiple explosive triggered size 2 storm slabs near Golden. Numerous naturally triggered storm slab avalanches were observed near Toby Creek, up to size 2 from alpine features on north facing slopes. Explosives also produced a size 1 storm slab avalanche confirmed to have failed on the late November surface hoar layer in the Toby Creek area. This layer also produced multiple natural avalanches up to size 2 on Sunday. This surface hoar layer is believed to be widespread in the Toby Creek drainage area above 1600m.

 A report on the Mountain Information Network noted a widespread natural cycle was evident in the Quartz Creek area. 

Several more storm slab avalanches up to size 1.5 were observed in the Northern Purcells throughout this storm. 

Snowpack Summary

Snowfall exceeds 80cm over the last week. More heavy precipitation and sustained strong winds will continue to build storm slabs over recently wind effected snow. Elevated freezing levels over the past week have created moist snow at lower elevations. 

A surface hoar layer has been observed down 30 to 40cm in the Toby Creek drainage in wind sheltered features. 

The mid-November rain crust exists throughout the region and sits down 30 to 60cm. It generally exists below 1900 m.

Several early season crusts exist throughout the lower snowpack and a late October facet/crust layer of concern sits at the bottom of the snowpack above 1900m. This layer has produced propagating results on recent tests, however data is sparse at this point in the season. 

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

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Avoid exposure to overhead avalanche terrain, avalanches may run surprisingly far.
  • Storm slabs in motion may step down to deeper layers resulting in 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.