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Avalanche Forecast

Archived

Mar 10th, 2022–Mar 11th, 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.

Flurries and moderate west winds may form small wind slabs at upper elevations later in the day. 

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

Confidence

High -

Weather Forecast

THURSDAY NIGHT: Increasing cloudiness / Light northwest winds / Low of -15 / Freezing level surface.

FRIDAY: Mostly cloudy with flurries in the afternoon; 3-10 cm, and another 5-10 cm overnight / Moderate west wind / High of -3 / Freezing level rising to 1000 m.

SATURDAY: Cloudy with isolated flurries; 3-5 cm / Light west wind / High of -1 / Freezing level 1400 m.

SUNDAY: Cloudy with isolated flurries; 3-5 cm / Light west wind / High of 0 / Freezing level 1500 m.

Avalanche Summary

Numerous skier triggered, size 1 wind slabs on primarily northerly aspects were reported on Wednesday. Additionally, a couple large cornice failures triggered slab avalanches on the slopes below up to size 3.

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

A few centimeters of recent snow now covers a weak layer of surface hoar in shady, sheltered terrain. The incoming snow this weekend will likely activate this layer. Recent west and northwest winds have formed wind slabs on lee features in the alpine. 

Sun crust on southerly aspects and temperature crust on all aspects below 1600 m.

The late February persistent weak layer combination of crust, facets and surface hoar is down 40-50 cm. Reports suggest this layer is becoming less reactive in most areas.

Two additional persistent weak layers from late January and mid-February are down 80-120 cm. They both consist of surface hoar and/or melt-freeze crusts. Recent trends indicate these layers have only been 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.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Carefully evaluate steep lines for wind slabs.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Cornice failure may trigger large avalanches.
  • Minimize your exposure time below cornices.

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.