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Avalanche Forecast

Archived

Dec 25th, 2022–Dec 26th, 2022

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

Regions

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

Increased winds, warmer temps, and new snow have added load to a very weak faceted snowpack.

The Christmas Eve Storm brought a spike in natural avalanche activity however this had already backed off with the fair weather Christmas Day. Incoming weather overnight promises to pack another punch for Boxing Day so further natural and human triggered avalanches should be expected.

A conservative approach to terrain is recommended through the holidays until things improve.

Confidence

Moderate

Avalanche Summary

Fresh wind slabs have been reactive to skier and explosive control in the past couple of days and many fresh natural slabs to sz 2.5 were observed Christmas day following the storm overnight.

Most of these slabs were size 1.5 with failures occasionally stepping down to trigger deeper slabs on the basal facets.

In steep to very steep terrain particularly treeline and below, we are getting reports of ski cuts or small slabs initiating long-running sluffs that entrain the unconsolidated facets found beneath the new snow.

Bourgeau left-hand went sz 2.5

Snowpack Summary

15 to 30 cm now sits over the December 17th layer of facets and surface hoar and has been redistributed to form windslabs in open areas by moderate to extreme west to south winds. The Nov 16 facet, crust and surface hoar layer is down 40-70 cm, just above the weak basal facets.

The snowpack is generally quite shallow and has been weakened by prolonged cold temperatures driving the faceting process. This is particularly true BTL where there is very little cohesion to be found in the snow which makes for poor support of travelers and for poor coverage of hazards.

Total snowpack depths at treeline range from 60-120 cms.

Weather Summary

As the next frontal system approaches overnight Sunday, flurries will produce 2-5cm of snow, alpine winds will increase to 40-60km/h, and alpine temperatures will fall to -10 to -15C. Monday, another trough will develop over Alberta which will draw winds alpine into the 60-80km/h range as the freezing levels reach 1300m and 2-5 cm of snow / rain? falls. Alpine temps will drop to -5/-10C overnight into Tuesday as another 2-5cm of snow arrives and the strong to extreme alpine winds remain.

Terrain and Travel Advice

  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • 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.

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.