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Avalanche Forecast

Archived

Dec 28th, 2021–Dec 29th, 2021

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

Regions

South Columbia.

The potential to trigger wind slabs and a buried weak layer are keeping the danger elevated.

Confidence

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

Weather Forecast

TUESDAY NIGHT: Mostly cloudy with isolated snowfall, accumulation 1 cm, 15 km/h north wind, alpine temperature -23 C.

WEDNESDAY: Clear skies with no precipitation, 15 to 30 km/h west wind, alpine temperature -21 C.

THURSDAY: Cloudy with snowfall, accumulation 5 cm, 20 to 40 km/h southwest wind, alpine temperature -22 C.

FRIDAY: Mix of sun and cloud with no precipitation, 15 km/h north wind, alpine temperature -22 C.

Avalanche Summary

A few wind and storm slab avalanches were triggered naturally and by riders on Tuesday. They were generally small to large (size 1 to 2), on all aspects, and at treeline and alpine elevations.

There have been a few reports of activity on the early-December weak layer described in the Snowpack Summary, including two natural avalanches and one triggered by a rider. They were generally large (size 2 to 3), on all aspects, and between about 1700 m and up to 2600 m.

Similar avalanche activity is possible for Wednesday, given similar weather conditions and cold temperatures limiting bonding of the snowpack.

Snowpack Summary

Cold air continues to facet the top of the snowpack. The cold air also means that old wind slabs found on all aspects could linger. There is potential for new wind slabs to start forming on Wednesday afternoon as the wind speed increases.

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

Sugary faceted grains may be found around the early-December melt-freeze crust 70 to 150 cm deep. The layer is most prevalent around 1700 m to 2400 m but could exist at lower and higher elevations for pockets 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 been most reactive where it remains shallower than about 100 cm. Learn more about how to manage this problem here.

Terrain and Travel

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Carefully evaluate steep lines for wind slabs.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • 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.