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Avalanche Forecast

Archived

Feb 18th, 2023–Feb 19th, 2023

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

Recent snow inputs and winds have loaded lee terrain creating fresh new slabs, developed cornices , and generated extensive loose dry sluffs out of very steep terrain ... all of these elements represent moving snow which provides the potential to trigger slabs.

Meanwhile the slabs overlying the persistent and particularly, the deep persistent, weak layers are showing signs that they have reached their tipping point and are ripe for triggering.

Climbers and Skiers alike should avoid overhead avalanche terrain and make very conservative terrain decisions should they choose to travel at all.

Confidence

Moderate

Avalanche Summary

A flight in the Northern part of the park Friday saw continued natural activity over the past 24 hours. Mainly wind slabs with some stepping down to persistent or deep persistent layers. Lake Louise observed a natural size 2.5 on "Speed run", and a natural size 3 in Richardson's bowl. Both initiated on the basal facets. As well, lots of recent explosive triggered and natural avalanches.

A size 2.5 deep persistent natural avalanche at Quartz ridge was triggered by a cornice on Thursday. There was also a MIN report of a skier remote triggering a size 2.5 avalanche in the Healy Creek area on Wednesday from 100m away showing continued reactivity to a skier's weight.

Snowpack Summary

10 to 25 cm of snow over the past 48hrs with moderate to strong SW-W winds have created extensive wind effect in the alpine and contributed to wind slab development. Several persistent weak layers exist 30-60cm below the surface. These weak layers include crusts, facets and surface hoar buried in January and are producing sudden test results in some locations. Deeper in the snowpack, the November crust/facet layer is found about 40 cm above the ground and also continues to produce sudden test results.

Weather Summary

Overnight into Sunday NW winds will strengthen to 50 to 60km/h and alpine temps will fall to -10 to -15C.

A low pressure system will impact the region Saturday with 5-10cm of snow, strong NW winds will shift W, temps will rise to -4 to -8C in the alpine during the day.

Overnight into Sunday, the cold front associated with the low will bring another 5 to 10 cm of snow and alpine temperatures will drop to -5 to -10C. Winds will weaken to 40 to 50km/h by morning.

A second westerly system will collide with cold northern air dropping down the prairies on Monday: significant snowfall is expected with dropping temperatures.

Terrain and Travel Advice

  • Make conservative terrain choices and avoid overhead hazard.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Cornice failure may trigger large avalanches.

Problems

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.

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.