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Avalanche Forecast

Archived

Jan 31st, 2020–Feb 1st, 2020

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

Regions

South Coast Inland.

Avoid avalanche terrain Saturday. Significant loading from snowfall, extreme wind and rain will maintain dangerous avalanche conditions through the day. There is potential for very large avalanches to run to valley bottom.

Confidence

High - We are confident about the likelihood of avalanche activity, what is less certain are their possible size. Uncertainty is due to whether buried persistent weak layers become active, triggering avalanches, with the arrival of the forecast weather.

Weather Forecast

Friday night: 30-40 cm new snow in the alpine for most areas, as high as 60 cm for the Coquihalla. Rain below 1300 m. Extreme southwest wind. Freezing level 1500 m.

Saturday: 10-20 cm new snow in the alpine for most areas, as high as 40 cm for the Coquihalla. Rain below 1300 m turning to snow as freezing levels drop. Strong southwest wind easing slightly. Freezing level dropping from 1500 m Saturday morning to valley bottom by evening.

Sunday: Mix of sun and cloud with isolated flurries. Light southwest wind. Alpine high -7 C. Freezing level valley bottom.

Monday: Mix of sun and cloud. Light northwest wind. Alpine high -7 C. Freezing level valley bottom.

Avalanche Summary

No avalanche observations on Friday due to poor visibility during the storm.

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

By Saturday morning, storm totals are forecast to reach 60-80 cm of heavy new snow, with another 10-20 cm falling though the day. Snow in the alpine is being ravaged by extreme wind. We suspect scoured windward aspects, hard slab in lee features and rapid cornice growth. At lower elevations new snow will overly a crust from the preceding rain as freezing levels drop through the day. 

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. The 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, deep avalanches to run full path or even longer.

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.