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Avalanche Forecast

Archived

Jan 29th, 2020–Jan 30th, 2020

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

Regions

South Coast Inland.

Watch for newly formed wind slabs in the alpine and open areas at treeline. Take advantage of the good riding in wind sheltered areas below treeline before the big warm-up arrives on Friday.

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

Wednesday night: Clear skies. Moderate west to southwest wind. Alpine low -10 C. Freezing level dropping to 500 m.

Thursday: Mix of sun and cloud with starting flurries in the afternoon. Southwest wind becoming strong, extreme at ridgetop. Alpine high -4 C. Freezing level 500 m rising to 1200 m.

Friday: 10-20 mm water equivalent in precipitation starting as snow, turning to rain below 1800 m. Strong southwest wind, extreme at ridgetop. Alpine high +2 C. Freezing level rising from 1500 to 2100 m.

Saturday: 10-30 mm rain overnight below 1500 m. During the day, up to 10 mm water equivalent in precipitation will start as rain, turning to snow as freezing levels drop. Moderate northwest to southwest winds. Freezing level dropping from 1800 m Saturday morning to valley bottom by Sunday morning.

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, Whitecap and Duffey Lake. 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 through Tuesday.

Snowpack Summary

30-60 cm sits over the Jan 20 crust below 2000 m. At upper elevations, the recent snow has been redistributed into wind slabs by strong 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, currently have no concerns about deep weak layers.

Terrain and Travel

  • Seek out wind sheltered terrain below treeline where you can avoid wind slabs and find great riding.
  • Be especially cautious as you transition into wind affected terrain.
  • 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.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

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.