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Avalanche Forecast

Archived

Dec 26th, 2020–Dec 27th, 2020

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

Regions

South Coast Inland.

Watch for fresh wind slabs at upper elevations and be mindful of the potential for wind slab avalanches to step down to deeper weak layers. 

If you see more than 15 cm of new snow in the Coquihalla area on Sunday morning, treat avalanche danger as CONSIDERABLE in the alpine.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

Saturday night: Up to 5 cm new snow, strong southwest wind easing to moderate, freezing level 500 m.

Sunday: Sun and cloud, light southwest wind, alpine temperature -7 C, freezing level 700 m.

Monday: Sun and cloud, light northwest wind, alpine temperature -3 C, freezing level 500 m.

Tuesday: Sunny, light northwest wind increasing to moderate southwest, alpine temperature -5 C, freezing level 300 m.

Avalanche Summary

Numerous skier triggered wind slab avalanches size 1-2 have been reported throughout the region over the last week. Typically they are being triggered on wind loaded convex terrain features at alpine and treeline elevations.

A few persistent slab avalanches have been triggered in the past week, mostly in the north of the region near the Hurley, but also near Allison Pass. They were triggered by riders, heavy machinery, and naturally. The slabs were generally 60 to 90 cm deep, around 2000 m, and released on the weak layers described in the snowpack summary.

Snowpack Summary

5-10 cm of new snow has been redistributed by strong overnight wind. Below treeline, the recent snow may be sitting over surface hoar.

A hard melt-freeze crust from early December is found around 40 to 120 cm deep in the snowpack. This crust may have weak layers above it, consisting of feathery surface hoar or sugary faceted grains. These weak layers are most prevalent in the north (e.g., Duffey Lake, Hurley) and found to a lesser extent in the south of the region. The snowpack should be treated as suspect anywhere you find either surface hoar or faceted grains above the crust.

The remainder of the snowpack is well-settled in the south of the region. In the north, another melt-freeze crust with associated faceted grains around it may be found near the ground. Without evidence of recent avalanche activity, the layer appears to be dormant at this time.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.

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.