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Avalanche Forecast

Archived

Dec 30th, 2021–Dec 31st, 2021

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

Regions

North Columbia.

Keep your eyes open for wind slabs in steep terrain features. There still remains the possibility of triggering a buried weak layer.

Confidence

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

Weather Forecast

THURSDAY NIGHT: Partly cloudy with no precipitation, 10 to 20 km/h north wind, alpine temperature -22 C.

FRIDAY: Clear skies with no precipitation, 10 to 20 km/h north wind, alpine temperature -22 C.

SATURDAY: Cloudy with snowfall, accumulation 2 to 5 cm, 20 to 40 km/h southwest wind, alpine temperature -18 C.

SUNDAY: Cloudy with snowfall, accumulation 10 to 20 cm, 30 to 60 km/h southwest wind, alpine temperature -14 C.

Avalanche Summary

A few small wind slab avalanches were observed in steep alpine terrain on Wednesday.

The latest avalanche activity on the early-December weak layer described in the snowpack summary was from Monday. This included two natural avalanches and one triggered by a rider. They were large (size 2 to 3), observed on all aspects, and found between 1700 m and up to 2600 m.

Snowpack Summary

Thin wind slabs may have formed from Wednesday night's 5 cm of snow and variable wind. These slabs could remain touchy to riders, as they sit on previously wind-affected snow, sugary faceted grains, and/or surface hoar in areas sheltered from the wind.

A weak layer of feathery surface hoar may be found around 30 to 50 cm deep. It is most likely found in sheltered terrain features in the lower alpine and treeline, or open features below treeline (e.g., cut blocks). Although avalanche activity hasn't been prominent on this layer, it has been reactive in snowpack tests.

Sugary faceted grains may be found around the early-December melt-freeze crust 80 to 150 cm deep. The layer is most prevalent around 1700 m to 2200 m but could exist at lower and higher elevations for sections of the region. This layer is spatially variable, with many areas showing good bonding to the crust whereas other areas showing concern. This layer has recently been most reactive where it remains shallower than about 100 cm.

Terrain and Travel

  • Carefully evaluate steep lines for wind slabs.
  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
  • 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.