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Avalanche Forecast

Archived

Feb 24th, 2022–Feb 25th, 2022

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

Regions

North Columbia.

Yellow means caution ! Wind slabs are still reactive to human triggering on all aspects, and buried weak layers remain suspicious on open slopes. Make sure to read the section Avalanche Problems.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

A strong ridge of high pressure will keep the region dry and cold until the weekend, with the potential for lingering valley clouds and an alpine temperature inversion. The next storm is expected late Saturday night as a shift in the weather pattern will occur.

Thursday night: Clear skies. Patchy valley cloud. Alpine temperatures around -20 C. Light northerly winds.

Friday: Mix of sun and clouds. Lingering valley cloud. Freezing level rising to 500 m. Alpine temperatures around -12 C. Light to moderate westerly winds.

Saturday: Increasing cloudiness. Flurries up to 5 cm in the afternoon. Freezing level rising to 800 m. Alpine temperatures around -8 C. Moderate to strong southwesterly winds.

Sunday: Snow 5-10 cm. Freezing level rising to 1100 m. Alpine temperatures around -6 C. Moderate to strong southwesterly winds.

Avalanche Summary

On Wednesday, a skier accidentally triggered a size 1 storm avalanche and took a ride on a previously skied slope in open trees just west of Revelstoke. See this MIN report for photos and details. Earlier this week, shifting arctic winds have redistributed the storm snow into wind slabs and a natural avalanche cycle occurred on southerly aspects. Several human-triggered wind and storm slab avalanches were also reported since then.

In the neighbouring region of South Columbia, two large persistent slab avalanches (size 3) were reported, one near London Ridge, and one from the Valhallas. They both occurred naturally on a south-westerly alpine slopes. These evidences are showing that, with added load to the snowpack from the last weekend’s storm, the mid-January weak layer began to "wake up". 

Snowpack Summary

Last weekend's storm brought 30-100 cm of new snow accompanied by southwesterly winds. Recent northeasterly has created a heavily wind-affected surface in exposed areas and redistributed storm snow into wind slabs in lee areas. Below ~1200 m the majority of the precipitation fell as rain, with 10-20 cm of snow now overlying a thick melt-freeze crust. 

Up to 120 cm now overlies a weak layer formed in mid-February. This layer consists of surface hoar in sheltered areas, a melt-freeze crust at lower elevations, a sun-crust on steep solar aspects, and hard wind-affected snow in the alpine and exposed treeline. Reports suggest that in many areas, the storm snow is bonding poorly to this firm layer.

The mid-January surface hoar/crust layer is now down 50-150 cm in the snowpack. There has been reactivity on this layer during last weekend's snowfall. See the avalanche summary for more details.

Terrain and Travel

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Closely monitor how the new snow is bonding to the old surface.
  • Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
  • Be aware of the potential for large avalanches due to the presence of buried persistent 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.