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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

South Columbia.

Yellow means caution ! Wind slabs are still reactive to human triggering on all aspects, and buried surface hoar 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 Sunday night as a shift in the weather pattern will occur.

Thursday night: Clear skies. Alpine temperatures around -15 C. Light to moderate northerly winds.

Friday: Mainly clear. Lingering valley cloud. Alpine temperatures around -10 C. Light to moderate northwesterly winds.

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

Sunday: Snow 5-10 cm. Freezing level rising to 1100 m. Alpine temperatures around -4 C. Moderate to strong southwesterly winds.

Avalanche Summary

Wednesday, in the Monashees, a skier accidentally triggered a large wind slab avalanche (size 1.5) on a steep treeline feature on a slope previously skied by 7 persons. Earlier this week, shifting arctic winds have redistributed the storm snow into wind slabs and a natural avalanche cycle occurred on southerly aspects. 

Persistent slabs were also observed lately, such as two large avalanches (size 3) reported near London Ridge and in the Valhallas. They both occurred naturally on south-westerly alpine slopes. This evidence is 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 20-80 cm of new snow accompanied by southwesterly winds. The north of the region received highest snowfall amounts, with tapering amounts to the south. 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 80 cm now overlies a weak layer formed in mid-February. This layer is comprised 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. This layer has started to 'wake up' following last weekend's snowfall. 

Terrain and Travel

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Keep your guard up at lower elevations. Wind slab formation has been extensive.
  • Use small low consequence slopes to test the bond of the new snow.
  • 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.