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

Regions

Northwest Inland.

Triggering avalanches remains likely on steep and wind loaded slopes, with the potential for large avalanches due to buried weak layers.

Confidence

Moderate - We are confident about the possible sizes of avalanches, should one release; what is less certain is the likelihood of triggering.

Weather Forecast

SUNDAY NIGHT: Mostly cloudy skies, moderate south wind, temperatures around -12 C.

MONDAY: Scattered flurries with a trace of new snow, strong south winds, temperatures around -8 C.

TUESDAY: Scattered flurries with 5-10 cm of snow throughout the day, strong south wind, temperatures around -5 C.

WEDNESDAY: Flurries continue with another 5-10 cm of snow, moderate south wind, temperatures around -5 C.

Avalanche Summary

Several natural storm slab avalanches were reported at Hankin on Sunday (see photos and details here). They were on northeast alpine slopes. The weekend's storm likely resulted in natural avalanche activity in alpine terrain across the region and has potentially left storm and persistent slabs reactive to human triggers.

Snowpack Summary

20-40 cm of snow has accumulated since New Year's Day, potentially leaving storm slabs in areas with deeper accumulations and wind affect. In some terrain this new snow may overly a weak and feathery surface hoar layer, particularly in sheltered treeline and below treeline terrain.

Around 50 to 100 cm deep, a hard melt-freeze crust from early December may have weak and sugary faceted grains around it. The last reported avalanche activity on this layer was around Dec 21. The likelihood of triggering this layer may have increased in response to the load of new snow.

The early-November melt-freeze crust may be found near the base of the snowpack and may have weak faceted grains around it. The last reported avalanche activity on this layer was near Smithers on Dec 22. The most likely terrain to trigger it would be in shallow and rocky alpine areas.

Terrain and Travel

  • Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
  • Be carefull around freshly wind loaded features.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • 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.

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.