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Avalanche Forecast

Archived

Mar 8th, 2023–Mar 9th, 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 possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

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

We've noticed several cornice failures over the last few days. These are likely triggered by solar radiation and generally triggering large avalanches on the slopes below.

As fresh lines become scarce, resist the urge to step into bigger terrain.

Confidence

Moderate

Avalanche Summary

Although avalanche activity is tapering, we are still seeing daily natural and explosive triggered avalanches. On Wednesday, field teams near Bow Lake observed a size 3 natural on a NW cross loaded aspect in the alpine that initiated as a windslab and stepped down to deeper layers.

LL ski hill triggered a size 2.5 on a reloaded bed surface for the 3rd time this season in steep alpine east facing terrain.

Likely triggers for natural avalanches are cornice failures and solar radiation and possibly both.

Snowpack Summary

Alpine and exposed treeline areas are wind effected with wind slabs that are slowly becoming less reactive. Steep solar slopes at treeline and below have a thin sun crust. The various Jan PWL interfaces of sun crusts, facets, and surface hoar are now down 40-80 cm. The weaker Nov. 16 basal facet layer is down 50-120 cm and produces moderate to hard sudden collapse results in tests.

Weather Summary

Stable weather continues on Thursday before a small system moves in on Friday. Consistent diurnal temperature swings with lows near -20, highs to -5 throughout the period.

Thursday: Clear and calm.

Friday: Snow starting near noon. 2- 5 cm with moderate NE alpine winds.

Saturday: Clearing with light NW winds.

For a more detailed weather forecast, click here.

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

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.

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.