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Avalanche Forecast

Archived

Jan 12th, 2023–Jan 13th, 2023

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 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.

Regions

Little Yoho, Field.

Warm and windy on Friday. Although there is only a few cm of snow in the forecast, it is a significant change in the weather. There is uncertainty as to if and how this weather will impact the deeper weak layers but confidence is low.

Confidence

Moderate

Avalanche Summary

No new avalanches observed or reported in the Little Yoho region.

Snowpack Summary

10-20 cm of loose snow sits over a denser mid-pack which has formed a slab over the weak facet layers below - this snow will create new wind slabs in lee areas. The December 17 weak layer is down 25-60 cm and becoming much less reactive in tests. The November 16 deep persistent layer of facets and depth hoar is near the base of the snowpack, continuing to show sudden failures. Profile from Ogden Bench on Wednesday.

Weather Summary

Expect warm and windy on Friday with up to 5cm in Little Yoho and 1500m freezing levels so above freezing in places like Field. Expect strong SW winds 60-80km/h diminishing to 50-60km/h over the day.

Terrain and Travel Advice

  • Uncertainty is best managed through conservative terrain choices at this time.

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.