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Avalanche Forecast

Archived

Mar 9th, 2022–Mar 10th, 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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Columbia.

Cornices are very large in many areas. Cornice failures may trigger large avalanches on the slopes below.

 Large skier triggered persistent slab avalanches have surprised riders in the southern Selkirk mountains over the past week. 

Confidence

High -

Weather Forecast

WEDNESDAY NIGHT: Mostly clear / Moderate northwest winds / Low of -20 / Freezing level surface.

THURSDAY: Mix of sun and cloud / Light northwest wind / High of -6 / Freezing level valley bottom.

FRIDAY: Mostly cloudy / Light northwest wind / High of -3 / Freezing level rising to 1100 m.

SATURDAY: Snow; 10-20 cm / Strong southwest wind / High of 0 / Freezing level 1500 m.

Avalanche Summary

Numerous skier triggered, size 1 wind slabs on primarily north and east aspects on Tuesday. Additionally, a size 2 natural cornice failure triggered a large (size 2.5) wind slab.

Over the past week we have seen the buried weak layers of surface hoar and crust from mid February and late January produce very large persistent slab avalanches up to size 3. Activity has been concentrated in the Valhalla, Goat, and Kokanee Ranges typically on north through southeast facing slopes at treeline elevations.

  • Multiple size 2-3 avalanches were remotely triggered from ridgeline features on Friday and Saturday, up to 90cm deep. 
  • A natural size 2 was triggered by solar input in the Valhallas on Friday. 
  • On Friday snowmobile triggered size 2 occurred near Slocan. Read the MIN report here for full details. 

The most likely triggers of these persistent slabs are large triggers such as smaller avalanches in motion, cornices, or snowmobiles.

Snowpack Summary

Recent west and northwest winds have formed wind slabs on lee features at treeline and above. These slabs may remain more reactive on south facing slopes where they are sitting on a slippery sun crust. Below the recent snow, there may be a layer of small surface hoar that is likely most pronounced on northerly aspects or sheltered locations.

Lower elevations have seen warm temperatures last week and have a melt-freeze crust on the surface below 1800 m.

The late February persistent weak layer combination of crust, facets and surface hoar is buried up to 50cm deep, and has been reactive mostly on south facing slopes during periods of sun. 

Two additional persistent weak layers sit 50-120 cm deep, from mid February and late January. They both consist of surface hoar and/or melt-freeze crusts. Recent trends indicate these layers have been more reactive in southern Selkirks around the Valhalla, Kokanee, and Goat Ranges. Several natural and human triggered avalanches have been produced on these layers in the last week. See the Avalanche Summary for full details.

Terrain and Travel

  • Cornice failure may trigger large avalanches.
  • Minimize your exposure time below cornices.
  • Carefully evaluate steep lines for wind slabs.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.

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.