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Avalanche Forecast

Archived

Dec 24th, 2021–Dec 25th, 2021

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

Regions

Purcells.

Flurries and wind will continue to develop slabs, expect to find more reactive deposits around ridges and in loaded terrain.

Confidence

Moderate -

Weather Forecast

Light to heavy snowfall is expected across southern BC Friday night through Sunday. An easterly arctic front meeting a southwesterly flow will produce enhanced snowfall where this clash occurs.

Friday night: Flurries 5-10 cm. Light and increasing southwest wind. Treeline temperatures near -16 and freezing levels at the valley bottom.

Saturday: Scattered flurries, 5-10 cm Moderate southwest wind. Treeline temperatures near -15 and temperatures dropping.

Sunday: Cloudy with scattered flurries, 5 cm. Light southwest wind and cold temperatures with a high of -20. 

Monday: Mix of sun and cloud. Light winds from the southwest and cold temperatures with a high of -24. 

Avalanche Summary

Explosives on Wednesday and Thursday triggered size 1-2 persistent slab avalanches at treeline elevations near Invermere, these failed on the crust-facet layer 40-70 cm deep.

On Wednesday, a few small (up to size 1) natural and human-triggered wind slab avalanches were reported. 

Snowpack Summary

20-40 cm of recent storm snow sits on a surface hoar interface, which was likely more preserved at treeline and below. Wind is impacting loose snow and stiffer slabs may exist on leeward slopes and in wind-loaded terrain features. Low-density storm snow exists in sheltered terrain.

The upper snowpack overlies a substantial crust from early December. This crust is approximately 60-120 cm below the surface, 10-30 cm thick on average, and is present across all aspects to at least 2300 m. A layer of weak facets (sugary snow) has been reported above this crust. Snowpack tests are generally showing hard results on this interface.

A late October facet/crust layer of concern sits at the bottom of the snowpack above 1900m. Although this layer has been trending less reactive, it remains on our radar.

The snowpack depth at treeline is around 120-250 cm. The deepest snowpack can be found in the southern half of the region. 

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Start with conservative lines and watch for clues of instability.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Dial back your terrain choices if you are seeing more than 20 cm of new snow.

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.