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Avalanche Forecast

Archived

Jan 28th, 2020–Jan 29th, 2020

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

Regions

South Coast Inland.

New snow and strong winds will form reactive windslabs on Wednesday. The new load will continue to stress deep weak layers which have been producing very large avalanches recently in the north half of the region.

Confidence

Moderate - Recent weather patterns have resulted in a high degree of snowpack variability within the region.

Weather Forecast

Tuesday night: Mostly cloudy. Alpine low -3 C. Southwest winds building to strong. Freezing level 1200 m.

Wednesday: 10-20 cm new snow. Alpine high -2 C. Strong southwest wind, approaching extreme at ridgetop. Freezing level 1400 m.

Thursday: Mix of sun and cloud with flurries in the evening. Alpine high -2 C. Light to moderate southwest wind. Freezing level 500 m rising to 1900 m in the evening.

Friday: Mix of sun and cloud with flurries in the evening. Alpine high +2 C. Moderate to strong southwest wind. Freezing level 2000 m.

Avalanche Summary

Reports of very large (size 3) deep persistent avalanches have been steadily coming in over the past week from the north half of the region. The most recent events occurred on Monday near Goldbridge and Whitecap. While most of these events have been naturals on north to east aspects in the alpine, some have been remotely triggered by skiers.

Natural wind slab avalanches size 2-2.5 were observed on wind-loaded slopes in the alpine on Sunday.

Snowpack Summary

30-60 cm sits over the Jan 20 crust below 2000 m. At upper elevations, the recent snow has been redistributed by strong southwest winds.

Two weak layer of note are isolated to the north half of the region, including the Duffey and Hurley areas. 1) A surface hoar layer is buried 1 m deep in sheltered areas around treeline. 2) A weak basal facet crust complex has been the failure plane in ongoing reports of deep persistent avalanches.The south of the region, including the Coquihalla and Manning areas, have no concerns about deep weak layers.

Terrain and Travel

  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
  • Wind slabs are most reactive during their formation.
  • Avoid freshly wind loaded terrain features.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.