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Avalanche Forecast

Archived

Jan 30th, 2020–Jan 31st, 2020

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

Regions

South Coast Inland.

Avoid avalanche terrain Friday. While heavy snowfall and extreme wind ravage the alpine, rain soaks the snowpack below 1800 m.

Confidence

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

Weather Forecast

Thursday night: 10-20 cm new snow, rain below 1200 m. Strong southwest wind, extreme at ridgetop. Freezing level 1200-1500 m.

Friday: 20-30 cm new snow in the alpine, rain line rising to 1800 m by mid afternoon. Extreme southwest wind. Freezing level rising from 1500 to 2100 m.

Saturday: 30-60 cm new snow, rain below 1300 m turning to snow as freezing levels drop. Moderate southwest wind. Freezing level dropping from 1500 m Saturday morning to 500 m by evening.

Sunday: Mix of sun and cloud with flurries bringing up to 5 cm new snow. Moderate southwest wind. Alpine high -5 C. Freezing level valley bottom.

Avalanche Summary

Observations were limited by poor visibility Wednesday, but some natural and explosive triggered storm slab avalanches were observed up to size 2.

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.

Snowpack Summary

30-50 cm of heavy new snow in the alpine is being ravaged by extreme wind. We suspect scoured windward aspects, hard slab in lee features and rapid cornice growth. Below 1800 m, the snowpack is becoming saturated by heavy rain.

In the north half of the region (ie. Goldbridge/Whitecap/Duffey/Hurley), a few deep instabilities exist in the snowpack, including a weak basal facet crust complex. This has been the failure plane in ongoing reports of deep persistent avalanches. Significant new loads from snowfall and rain will stress the deep basal weakness.

The south of the region, including the Coquihalla and Manning areas, currently have no concerns about deep instabilities.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • Be aware of the potential for large, destructive avalanches due to the presence of deeply buried weak layers.
  • Be aware that wet activity at low elevations is a classic situation for step-down failures in deeply buried persistent weak layers.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.