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Avalanche Forecast

Archived

Jan 10th, 2020–Jan 13th, 2020

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 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

North Rockies.

New snow and variable wind will form wind slabs in exposed terrain on all aspects. Caution is also warranted in sheltered terrain features, as a buried weak layer could still be triggered.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

FRIDAY NIGHT: Cloudy with light snowfall, accumulation 2 to 5 cm, light to moderate west wind, alpine temperature -16 C.

SATURDAY: Cloudy with light snowfall, accumulation 2 to 5 cm, light to moderate northwest wind, alpine temperature -22 C.

SUNDAY: Mix of sun and cloud, light northeast wind, alpinee temperature -30 C.

MONDAY: Clear skies, light northeast wind, alpine temperature -35 C.

Avalanche Summary

A few large, destructive were recently reported near the McGregors, suspected to have failed naturally on the weak layer described in the snowpack summary. They occurred on southerly aspects and at an elevation of 1500 m.

A few storm slab avalanches were also reported to have failed from human activity in recent storm snow.

Snowpack Summary

Around 10 to 20 cm of new snow may accumulate from Friday to Saturday. This will create relatively soft conditions in sheltered terrain but potentially wind slabs in exposed terrain. The wind will change directions from the southwest to the northeast by Sunday, meaning that wind slabs may be found on all aspects.

The main layer of concern is a feathery surface hoar layer that was buried around Christmas. The depth of this layer varies and could be found from about 50 cm deep to 150 cm deep. While this layer was very reactive last week, recent reports suggest that its reactivity is localized to certain parts of the region. There has been more recent evidence of this problem in the southern parts of the region around McBride and the McGregors, but preserved surface hoar could potentially be found on sheltered slopes anywhere in the region.

Terrain and Travel

  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Surface hoar distribution is highly variable. Avoid generalizing your observations.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • Choose gentle slopes without steep terrain above.

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.