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Avalanche Forecast

Archived

Feb 10th, 2022–Feb 11th, 2022

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

Regions

North Columbia.

Conditions are trickier than meets the eye. Warm temperatures and strong solar radiation will test the snowpack on south-facing aspects, while a buried persistent weak layer continues to surprise riders at mid-elevations on north-facing terrain. 

Confidence

Low - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather. Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

A building ridge of high pressure will usher in clear skies and warm temperatures. 

Thursday Overnight: Clearing. Ridge winds 20-60km/h from the northwest. Freezing level dropping to valley bottom.

Friday: Mainly clear. Ridge winds 20-40 km/h from the west. Freezing level rising to 1500 m.

Saturday: Mainly clear. Ridge winds 10-40 km/h from the northwest. Freezing level rising to 1700 m.

Sunday: Increasing cloud cover. Light ridgetop winds. Freezing level rising to 2000 m.

Avalanche Summary

Over the past week, a persistent weak layer of buried surface hoar has produced numerous large human-triggered avalanches, surprising both professionals and recreationists. This layer has shown the most reactivity between 1600-2200 m, with the most reactivity observed in open areas in the trees, in cut blocks and on steep convexities. Check out some good example photos here. Compelling observations on this layer in the neighbouring Glacier National Park can be seen here. 

Snowpack Summary

Overnight, clear skies and cooling temperatures will refreeze the surface of the snowpack at lower elevations where it has been affected by rain and warm temperatures. A sun crust has formed on sun-exposed slopes at all elevations. In the alpine and exposed treeline, strong winds throughout the week have created a variety of wind-affected surfaces. Expect to find old and new wind slabs on a variety of aspects, with the most recent and reactive slabs formed in terrain features lee to the northwest. 

A weak layer of surface hoar exists 60 to 100 cm deep in the snowpack, which is a prime depth for human triggering. The layer is most prominent in areas sheltered from the wind. Example terrain features to treat as suspect include the lee side of protected ridges, openings in the trees, cut blocks, and burns. The layer may not exist on steep sun-exposed slopes, where a melt-freeze crust may be found instead.

The facet/crust layer that formed in early December is buried around 120 to 250 cm. The last reported avalanche was on January 31 from a large explosive, and before that on January 23. Although unlikely, the layer could be triggered from a large load like a cornice fall or a shallower slab avalanche could step down to this layer. Humans are unlikely to trigger it, with perhaps the exception in thin, shallow snowpack areas. Check out the forecaster blog for more information.

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Surface hoar distribution is highly variable. Avoid generalizing your observations.
  • Cornice failure may trigger large avalanches.
  • Uncertainty is best managed through conservative terrain choices at this time.

Problems

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.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.