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Avalanche Forecast

Archived

Dec 28th, 2020–Dec 29th, 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, 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 Coast Inland.

A small chance of triggering a deeper weakness remains. Continue to avoid high consequence terrain to account for this possibility.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Monday night: Dry with clear skies. Cooling temperatures.

Tuesday: 2-5 cm new snow. Treeline temperatures around -14 C. Winds light to moderate southwesterly. 

Wednesday: 4-8 cm new snow. Treeline temperatures around -6 C. Winds moderate southerly. 

Thursday: Flurries. Treeline temperatures around -7 C. Winds light southwesterly.

Avalanche Summary

A size 1 wind slab avalanche was reported from an east aspect on Cayoosh on Sunday. Storm slabs and loose dry avalanches were also reported from Chief Pascal on the Duffey and on the Yak/Nak col along the Coquihalla.

A few persistent slab avalanches were reported last 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

5-15 cm of recent snow has seen some redistribution by wind, resulting in good riding quality on lee aspects in the Coquihalla area, according to the great MIN reports we've received. (If you're going out in the Duffey, please share your observations on the MIN!) Below treeline, 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

  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.

Problems

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.

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.