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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

South Columbia.

Wind slabs up high and the potential to trigger 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

THURSDAY NIGHT: Partly cloudy with no precipitation, 10 to 20 km/h northwest wind, alpine temperature -21 C.

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

SATURDAY: Increasing clouds with afternoon snowfall, accumulation 1 to 3 cm, 20 to 40 km/h southwest wind, alpine temperature -17 C.

SUNDAY: Cloudy with snowfall, accumulation 5 to 10 cm, 30 to 60 km/h southwest wind, alpine temperature -14 C.

Avalanche Summary

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.

The latest persistent slab avalanche occurred on Tuesday, 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

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). 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

  • 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.