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Avalanche Forecast

Archived

Jan 26th, 2023–Jan 27th, 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, human triggered possible.

Regions

Glacier.

Warm temps, fresh storm snow and gusty winds are a perfect combo for building reactive slabs.

Watch for signs of instability, such as recent avalanches, shooting cracks, hollow sounds and whumphing.

Confidence

Moderate

Avalanche Summary

Thursday: Small cycle of natural activity along the highway corridor, up to size 2.5, primarily in steep N facing terrain off Mt. Macdonald. Triggered by consistent moderate winds.

Wednesday: Skier accidental from McGill shoulder, triggered on the surface hoar down 50cm. Parks Canada staff triggered soft slabs, up to size 1, down 30-40cm on a sun crust at treeline. And sluffing in steep terrain.

Wednesday: small natural cycle, size 2-2.5, along the highway corridor from south facing terrain. Triggered by wind loading and sun effect midday.

On Monday, both natural and skier triggered avalanches were observed on wind slabs.

Snowpack Summary

Wind slabs in the alpine and treeline on lee features. Warm storm snow is building a slab with moist snow/crusts below 1700m and sun crusts on steep, solar facing terrain. This sits on top a Jan 21 sun/temperature crust down ~30-40cm.

The Jan 3 surface hoar, which most likely to be rider triggered at treeline, is down 50-70cm.

The mid-pack facets are slowly rounding and gaining strength, while the basal facets and Nov 17 facet/SH/crust weakness are still reactive when isolated in snowpack tests.

Weather Summary

A final cold front moving over the region will bring snow through Friday. A cold, dry arctic air mass will arrive on the weekend.

Tonight: Snow, 5-10 cm, Alp Low -6*C, 1000m Freeze Level, Light to Mod W winds.

Fri: Cloudy w/flurries, Alp high -5*C, 1200m FZL, Light to Mod N winds

Sat: Sunny, Alp high -17*C, FZL, Valley Bottom, Light NE wind.

Terrain and Travel Advice

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

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.