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Avalanche Forecast

Archived

Mar 1st, 2020–Mar 2nd, 2020

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

Regions

South Coast Inland.

Strong winds and incremental snowfall are expected to continue to build wind slabs at upper elevations. In the northern part of the region, buried weak layers require careful evaluation and terrain selection.

Confidence

Moderate - Uncertainty is due to the limited number of field observations. Uncertainty is due to extremely variable snowpack conditions reported through the region.

Weather Forecast

Sunday: Cloudy, up to 5 cm of snow, strong southwest winds, freezing level 500 m. 

Monday: Mostly cloudy, up to 5 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 rising to 1500 m.

Wednesday: Decreasing cloud, 5-10 cm of snow overnight, strong southwest wind decreasing to light, freezing level 1000 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, with 30+cm in the south of the region (i.e. Coquihalla). Strong southwest winds have been redistributing the storm snow into wind slabs on lee features at upper elevations and rapidly loading cornices. 

In the northern part of the region (i.e. Duffey/Hurley/Goldbridge), a weak layer of sugary faceted snow and feathery surface hoar from February 22 may be buried 40-70 cm deep and warrants careful evaluation. There is high uncertainty regarding the distribution of this weak layer in the region. However, where it does exist, conditions may be prime for human-triggering. Check out the latest forecaster blog that offers a deeper dive into these conditions.

Also 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

  • Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.

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.