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Avalanche Forecast

Archived

Feb 23rd, 2020–Feb 24th, 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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
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.

Regions

South Coast Inland.

Recent snow rests on a weak layer so it may take longer than usual to bond to old surfaces and will likely remain reactive to human traffic. Continue to make conservative terrain choices while storm snow settles and stabilizes.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Sunday night: Around 15 cm new snow in the south of the region, trace in the north. Strong northwest wind. Freezing level dropping from 1000 m to valley bottom.

Monday: Mix of sun and cloud. Moderate northwest wind. Freezing level 800 m.

Tuesday: Mix of sun and cloud. Moderate to strong southwest wind. Freezing level 1000 m.

Wednesday: Mix of sun and cloud. Light to moderate southwest wind. Freezing level 1400 m.

Avalanche Summary

Natural storm slab and loose dry avalanches to size 1.5 were observed in the north of the region Saturday.

Snowpack Summary

20-40 cm of recent snow sits over a layer of widespread surface facets, surface hoar in sheltered areas or sun crusts on solar aspects. Recent avalanche activity indicates a poor bond at this interface. In the alpine and exposed treeline, recent snow has been redistributed by strong southwest to northwest wind, loading deep deposits into lee features.

In the north part of the region (e.g. Duffey/Hurley/Goldbridge), a deep instability exists in the snowpack, consisting of a weak basal facet-crust complex. Sporadic avalanche activity on this layer is keeping it on our radar, with the latest report described here. In the south of the region, including the Coquihalla and Manning areas, there are no concerns about deeply buried weak layers.

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
  • If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.

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.