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Avalanche Forecast

Archived

Jan 8th, 2023–Jan 9th, 2023

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

Banff Yoho Kootenay, Banff, East Side 93N, Kootenay, Lake Louise, LLSA, Sunshine, West Side 93N, Field.

Forecasters remain concerned about the potential for human triggering of the buried facet layer at the base of the snowpack. Continued discipline in sticking to mellower terrain with low consequences is the most reliable method of reducing risk in these conditions.

The deep persistent slab problem in particular has shown potential for long propagations and remote triggering.

Confidence

Moderate

Avalanche Summary

No new natural avalanches were reported or observed on Saturday or Sunday. Skier triggered whumpfing and cracking continue to occur in many places. Local ski hills have had explosive triggered avalanches up to size 2 on both of the buried facet layers near the base of the snowpack in the past several days.

Snowpack Summary

Some wind-affected snow on alpine and treeline ridgetops. 10-20 cm of softer surface snow sits over a denser mid-pack which has formed a slab over the weak facet layers below. The December 17 persistent layer of surface hoar/facets is down 25-60 cm and becoming less reactive. The November 16 deep persistent layer of facets, depth hoar, and/or sun crusts is found near the base of the snowpack with test results continuing to show sudden failures.

Weather Summary

A mix of sun and cloud with light flurries along the divide will continue into Monday. Winds will increase from the SW on Sunday night before dropping back to the light-moderate range on Monday. Temperatures will remain relatively mild on Monday, with daytime highs near -3°C at the valley bottom and alpine temperatures between -8 and -12°C.

Terrain and Travel Advice

  • Uncertainty is best managed through conservative terrain choices at this time.
  • Use careful route-finding and stick to moderate slope angles with low consequences.

Problems

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.

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.