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Avalanche Forecast

Archived

Dec 29th, 2021–Dec 30th, 2021

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

Regions

South Columbia.

New wind slabs are expected to form on Wednesday night. Sporadic reports of avalanches on a couple buried weak layers are keeping our guard up.

Confidence

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

Weather Forecast

WEDNESDAY NIGHT: Cloudy with snowfall, accumulation 5 to 10 cm, 20 to 50 km/h southwest wind, alpine temperature -21 C.

THURSDAY: Mostly cloudy with isolated flurries, trace accumulation, 10 to 20 km/h northwest wind, alpine temperature -20 C.

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

SATURDAY: Increasing clouds with snowfall, accumulation 5 cm, 40 to 60 km/h southwest wind, alpine temperature -15 C.

Avalanche Summary

A few small (size 1 to 2) avalanches were triggered naturally and by riders on Tuesday. They occurred within the top 50 cm of the snowpack, with at least a couple of them occurring on the surface hoar layer described in the snowpack summary. They were mostly on west to northeast terrain features at treeline to alpine elevations.

Another persistent slab avalanche was observed, occurring in alpine terrain on a northeast aspect. It was very large (size 3 to 4) and indicates that this layer remains capable of forming large and destructive avalanches.

Snowpack Summary

A bit of new snow and strong wind are likely to form new wind slabs in exposed terrain Wednesday night. These slabs will overly previously wind-affected snow, sugary faceted grains, or surface hoar. 

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. Only a couple small avalanches have been reported on this layer but it is showing reactivity in 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 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 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.