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Avalanche Forecast

Archived

Feb 22nd, 2020–Feb 23rd, 2020

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

Regions

South Coast Inland.

Avalanche danger will increase as touchy storm slabs build through the day Sunday.

Confidence

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

Weather Forecast

Saturday night: Flurries bringing a trace of new snow. Light to moderate southwest wind. Freezing level 1000 m.

Sunday: 10-25 cm new snow with lightest accumulations in the Duffey. Strong southwest wind. Freezing level 1000 m.

Monday: Overnight snowfall up to 10 cm of new snow in most areas and 20 cm for the Coquihalla. Mix of sun and cloud. Light to moderate northwest wind. Freezing level 700 m.

Tuesday: Mix of sun and cloud. Light to moderate southwest wind. Freezing level 1300 m.

Avalanche Summary

Natural storm slab and loose dry avalanches to size 1.5 were observed in the Duffey on Saturday.

Snowpack Summary

10-25 cm of new snow will fall through the day Sunday. Forecast strong southwest winds are expected to redistribute the new snow at alpine and treeline elevations, loading lee terrain features. 20-30 cm of recent snow now sits over a layer of widespread surface facets, surface hoar in sheltered areas or sun crusts on solar aspects. Storm slabs are expected to slide easily on these weak layers.

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

  • Use increased caution at all elevations. Storm snow is forming touchy slabs.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.
  • Good day to make conservative terrain choices.

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.