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Avalanche Forecast

Archived

Mar 2nd, 2020–Mar 3rd, 2020

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

Strong winds and incremental snowfall continue to build wind slabs at upper elevations. Deeper instabilities cannot yet be discounted.

Confidence

Moderate - Uncertainties in both the snowpack structure and the weather forecast limit our confidence. Uncertainty is due to the limited number of field observations.

Weather Forecast

Monday night: Mostly cloudy, 3-8 cm of snow, strong southwest winds, freezing level 1300 m.

Tuesday: Mix of sun and cloud, scattered flurries with up to 5 cm of accumulation, strong southwest winds, freezing level 1400 m.

Wednesday: Mix of sun and cloud, 5-10 cm of snow overnight, moderate southwest wind decreasing to light, freezing level 1000 m.

Thursday: Mostly cloudy, up to 5 cm of snow, 10-15 cm possible near the Coquihalla, strong southwest wind, freezing level rising to 1500 m.  

Avalanche Summary

Over the weekend, recent small (size 0.5-1.5) wind slab avalanches were reported breaking 20-30 cm deep on lee features near and above treeline. 

Periods of strong solar radiation on Saturday initiated pinwheels, rollerballs, and small wet loose avalanches on steep, sunny slopes.

Snowpack Summary

Incremental snowfall and strong winds from the southwest are expected to continue to build reactive wind slabs at upper elevations. 20-30 cm of snow has accumulated since Friday (30+cm near the Coquihalla), with winds redistributing the storm snow into slabs on lee features and rapidly loading cornices. 

A weak layer of sugary faceted snow (and possibly feathery surface hoar in isolated areas) from February 22 may be found 40-70 cm deep. Although there has been little avalanche activity on this layer, recent snowpack test results suggest that a propensity for human triggering may still linger. See this MIN for a helpful illustration.

In the northern part of the region (i.e. Duffey/Hurley/Goldbridge), a deep instability exists at the base of the snowpack. It has not produced recent avalanche activity since February 17th. Rapid warming or heavy loading by new snow/wind/rain events have the potential to re-awaken this layer.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.