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Avalanche Forecast

Archived

Nov 19th, 2024–Nov 20th, 2024

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

Regions

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

Up to 10cm of new snow and accompanying wind is forecasted to arrive Wednesday. Watch for fresh wind-slab development. Additionally, a deep persistent slab problem is evolving on the Oct 23 crust layer. Keep this in mind moving forward.

Confidence

Moderate

Avalanche Summary

Lake Louise Patrol reported another deep slab release on the October 23 crust, triggered by explosives. The slide was a size 2. Sunshine patrol observed a size 2 cornice triggered wind slab on an alpine lee feature on Healy Peak. The Visitor Safety field team did not observe any avalanches on 93N.

Snowpack Summary

A few cms of snow over previous wind slabs in exposed alpine and treeline terrain. In the middle of the snowpack the Nov 9 solar/temp crust is present. In some places there is surface hoar on this crust making it more reactive to loading. At the base of the snowpack a crust that formed in late October can be found to ridgetop. Facets are developing around this basal crust. Treeline snow depths range from 40-60 cm with less snow at lower elevations and many thinly buried hazards.

Weather Summary

5-10cm of snow will accumulate in the region late Wednesday into Thursday. Temperatures will be generally seasonal, with valley temperatures below 0 and the ridge near -12. The leading edge of the front will be windy, with values as high as 80km/hr from the south, but it will be short-lived and taper off into the moderate range on Thursday.

Terrain and Travel Advice

  • Watch for newly formed and reactive wind slabs as you transition into wind-affected terrain.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

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.

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.