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Avalanche Forecast

Archived

Dec 31st, 2021–Jan 1st, 2022

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

Regions

South Columbia.

Keep an eye on the wind. Avalanche hazard will likely increase throughout the day as the strong winds build small but reactive slabs.

Confidence

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

Weather Forecast

Friday night: light northwest winds with no new snow expected. Low of -27 at 1500m,

Saturday: Moderate to strong west winds with up to 5cm of new snow. High of -15 at 1500m.

Sunday: strong southwest winds in the alpine with light snow all day accumulating up too 10cm with the largest snowfall amounts in the Monashees. High of -14 at 1500m.

Monday: light snow all day with light to moderate southwest winds in the alpine. High of -7 at 1500m.

Avalanche Summary

Recently a size 2.5 natural avalanche was reported in the Selkirks. This avalanche was on a northwest aspect at 2100m and failed on the early December facet crust combo. The crown was up to 150cm deep, a good indicator of the deadly consequences of being involved in an avalanche failing on this deep layer.

Numerous small to large (size 1 to 2) slab avalanches were triggered naturally and by riders on Wednesday. They occurred on all aspects, were often 10 to 40 cm deep, and generally at treeline and alpine elevations. A few of the avalanches were wind slabs, and it is possible that some of the others released on the surface hoar layer described in the snowpack summary.

Snowpack Summary

New wind slab will form throughout the day on Saturday on north and east aspects. These new slabs will form over faceted and wind effected surfaces, this will likely result in a poor bond.

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). To date, this layer has been most active in the southern half of the region.

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 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

  • 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.
  • Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.

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.