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Avalanche Forecast

Archived

Feb 28th, 2020–Feb 29th, 2020

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

Regions

South Coast Inland.

Winds are strong and shifting direction as snow accumulates, creating a tricky pattern of wind slabs at upper elevations. Use caution around drifted slopes and convex roll-overs.

Confidence

Moderate - Uncertainty is due to the track & intensity of the incoming weather system.

Weather Forecast

Friday night: Cloudy, 5-10 cm of snow, closer to 20 cm for the Coquihalla, strong southwest winds switching to northwest, freezing level dropping to valley bottom.

Saturday: Mostly cloudy, up to 5 cm of snow, moderate northwest winds, freezing level 1000 m.

Sunday: Mostly clear, light variable winds, freezing level 1200 m. 

Monday: Partly cloudy, isolated flurries with trace accumulations, moderate southwest winds, freezing level 1300 m. 

Avalanche Summary

No recent avalanches have been reported. Some minor snowballing was observed on steep, sunny slopes Wednesday and Thursday across the region. 

On Monday and Tuesday, several small to large (size 1.5-2) natural and human-triggered wind slab avalanches were observed on northeast, northwest, and west aspects in the alpine breaking 10-50 cm deep. 

Snowpack Summary

By Saturday afternoon, 5-15 cm of snow is forecast to accumulate (with up to 20 cm possible along the Coquihalla) as the freezing level drops to valley bottom. Strong winds from the southwest are expected to switch to the northwest and decrease. This will likely create a complex pattern of reactive wind slabs on lee features at upper elevations.

Earlier in the week, 15-40 cm of snow buried an interface of near surface facets and sun crusts. The surface hoar associated with this interface in other regions reportedly has a more spotty distribution in this region, and it may persist in isolated areas (sheltered open slopes near and above tree line).

In the north part of the region (ie. Duffey/Hurley/Goldbridge), a deep instability exists at the base of the snowpack. It has not produced recent avalanche activity, with the most recent event on February 17. Rapid warming or heavy loading by new snow/wind/rain events has the potential to re-awaken this layer.

Terrain and Travel

  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.

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.